DE29520066U1 - Compensation current conversion device - Google Patents

Description

Description

Device for compensation current conversion

The invention relates to a device for compensating current conversion, consisting of a magnetic field sensor, a subsequent regulator stage, two amplifier stages, which are designed as push-pull output stages, which are in particular symmetrically fed, and a load in the form of a resistor, across which a voltage proportional to an input current drops.

Compensation current transformers, which are generally used to convert large currents in the ampere range into proportionally smaller currents, have the disadvantage in the conventional design mentioned above that the primary current to be converted is limited upwards due to the design. The limiting criterion for the maximum primary current that can be represented is the internal resistance of the compensation winding, which, like the primary current to be measured, is mounted on a common magnetic core. The compensation winding and thus its internal resistance in turn depends on the available winding space of the magnetic core used.

If you want to make better use of the compensation current transformer, for example by applying higher input currents to smaller compensation current transformers in order to avoid larger transformers and thus save space and costs, the power consumption for the compensation winding increases and, accordingly, the power loss in the control system. This problem also arises, for example, with compensation current transformers in which push-pull operation is provided, whereby the input current that can be processed is doubled without changing the size. Such a device is described in G 295 07 675.

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However, doubling the compensation current and the applied voltage results in four times the power being supplied. In normal operation, however, a large part of the supplied power is converted into heat at the push-pull output stage. As with a series regulator, the voltage that is not required appears as a loss voltage across the push-pull output stage. As a product with the compensation current, this power loss is constant over a wide operating range.

Traditionally, this problem of increased power requirements is addressed by using larger power supplies and control electronics with more powerful output stages and larger cooling surfaces. This results in higher costs and does not solve the problem of power loss as such. It is simply dissipated.

Another approach is to shift part of the power loss from the control electronics to a series resistor, which is connected in series with the load resistor. However, this does not prevent the fact that power loss occurs. This is also simply dissipated.

The object of the invention is therefore to improve a device for compensating current conversion of the type mentioned at the beginning in such a way that the power loss that occurs is minimized. In this case, commercially available standard components, which are particularly inexpensive due to their high availability, should continue to be usable wherever possible.

According to the invention, this object is achieved in that 1.1 means are provided for clocking the amplifier stages, 5 1.2 the inductance of the compensation winding serves for smoothing.

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In a first advantageous embodiment of the invention, a particularly advantageous frequency range is specified, which allows an optimal minimization of the power loss. This is achieved by

2.1 the clock frequency is specified in the range between 100 kHz and 200 kHz.

In a further advantageous embodiment of the invention, the clock frequency is generated with particularly advantageous use of existing components. This is achieved by

3.1 the clock frequency can be derived from an oscillator provided for exciting the magnetic field sensor.

In a further advantageous embodiment of the invention, a particularly effective further processing of the clocking takes place, whereby already existing components are used for implementation, which enables a particularly inexpensive solution. This is brought about by the fact that

4.1 the clocking is pulse width modulated.

In a further advantageous embodiment of the invention, the pulse width modulation can be varied by

5.1 two comparators are provided for setting the pulse-pause ratio.

In a further advantageous embodiment of the invention, a particularly effective solution for a compensation current transformer is created with few circuitry measures by

6.1 the load resistance is designed as a floating load via a subsequent differential amplifier. 35

In a further advantageous embodiment of the invention, the newly added modules are particularly easily integrated into

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the existing concept of the type mentioned above is integrated and inexpensive standard modules are used. In addition, the connection of the additional modules is carried out in a particularly simple manner. This is solved by

7.1 the load in the form of the resistor is connected between the outputs of the push-pull output stage,

7.2 the burden in the form of the resistor is connected between the two inputs of the differential amplifier.

A further advantageous embodiment of the invention prevents the so-called "latch up" criterion from being exceeded when the compensation current transformer according to the invention is fully utilized. This prevents the compensation current from being too high when switched on due to different increases in the positive and negative supply voltage and uncontrolled overshoots in the regulator stage, and as a result the electronics of the evaluation stage may also go into the "latch up" state. This is prevented by

8.1 the regulator stage and/or push-pull output stage are controlled by a latch-up control, which in particular monitors the symmetry of the positive and negative supply voltage and the regulator sum point for 5 irregular values.

A further advantageous embodiment of the present invention enables the construction of a particularly effective compensation current transformer, which enables a particularly cost-effective construction of the compensation current transformer on the input side due to a particularly favorable arrangement of the components. This is achieved by

9.1 the primary current is guided with a winding through a magnetic toroidal core, in particular one with an air gap,

9.2 the compensation current is guided through several windings through the same magnetic toroidal core.

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A further advantageous embodiment of the present invention enables the construction of a particularly small-sized compensation current transformer, which enables the advantages according to the present invention in a particularly space-saving and thus inexpensive manner. This is achieved by

10.1 it can be integrated into a user-specified integrated circuit.

The advantages achieved with the invention are in particular that the increased power loss that occurs due to a special structural design of the compensation current transformer for higher input currents is not only dissipated, but is minimized. This is achieved by particularly clever circuit measures with multiple use of existing components. The use of commercially available standard modules designed for common supply voltages is also still possible. In this way, complex special solutions for the power supply and evaluation electronics can be avoided.

Further details and advantages emerge from the embodiment of the invention described below and from the drawing. 5 shows:

FIG 1 shows a circuit arrangement of a compensation current transformer with a pulse width modulated clocked push-pull output stage with "floating" burden and "Latch 0 up" control.

The illustration in the figure shows a circuit arrangement of a compensation current transformer with a pulse width modulated clocked push-pull output stage for minimizing power loss and latch-up control. In this case, a primary current il is measured by a magnetic field sensor S by passing the primary current il through a magnetic ring core RK

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with an air gap. The primary current il is detected by a T-field probe T arranged above the air gap and fed to a regulator stage R. The value determined there, which represents the compensation current ia, is then fed to a push-pull output stage G, which is fed by a symmetrical voltage supply with positive voltage P15 and negative supply voltage Nl5 of 15 V. However, this does not happen directly, but via two comparators Cl and C2, each of which has a negated and a non-negated output. The comparators are preferably constructed using operational amplifiers. The output signal of the regulator stage R, which is proportional to the compensation current ia, is fed to one of the comparators at its inverting input and to the other comparator at its non-inverting input. In the present embodiment, the output signal of the regulator stage R is applied to comparator C1 at the inverting input and comparator C2 at the non-inverting input.

0 The frequency f required for clocking, which is preferably in the frequency range between 100 kHz and 200 kHz, but can also include other frequencies - depending on the dimensioning of the compensation current transformer - is obtained from the existing control and evaluation electronics, which are not shown in detail in the illustration according to FIG 1 for the sake of clarity. This control and evaluation electronics usually has an oscillator O for exciting the T-field probe T. However, if such an oscillator O is not provided, it is added separately.

In addition to this oscillator O, from which the required frequency f is derived, there is an integrator I which is controlled by the frequency signal f and which generates a triangular signal which is shown at the output in the illustration in FIG 1. This integrator I can, for example, be constructed from an RC element.

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The two comparators Cl and C2 are supplied with the triangular signal from integrator I at their as yet unconnected inputs. The comparators Cl and C2 are thus used to generate pulse-pause signals. The pulse-pause ratio can be determined at a constant frequency of the triangular signal using the voltage value applied to the second input of the comparators, which can be specified and varied by the controller R. The comparators Cl and C2 have dead times relative to one another and are locked against one another so that opposing transistors in the push-pull output stage G cannot switch through at the same time. This push-pull output stage G can be designed as a bridge output stage and bipolar transistors or MOSFETs, for example, can be used as output stage transistors. The push-pull output stage G is controlled by the output signals of the comparators Cl and C2 in such a way that one of the outputs of the push-pull output stage G has a positive output voltage P15 and the other output has a negative output voltage N15. The polarity changes with the pulse-pause alternation in time with the frequency f. With the pulse-width modulated clocking of the push-pull output stage G thus achieved, only comparatively low conduction and switching losses occur, which significantly reduces the power loss.

5 The compensation current ia is led from an output of the push-pull output stage G with several turns over the magnetic ring core R. The number of turns of the conductor carrying the compensation current ia is many times greater than the number of turns of the conductor carrying the primary current il. The compensation current ia led over the magnetic ring core RK is then fed to a load in the form of an electrical resistance Rb. The average voltage value specified by the regulator stage R is set by a corresponding pulse-pause ratio and the high inductance of the compensation winding, which is usually between 300 and 1600 mH, ensures that the current is smoothed. This ensures that the compensation current that is already present is

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Current winding is used without additional effort for a further positive effect.

The load resistance Rb is conventionally connected to ground potential M. The device according to the invention of a compensation current transformer avoids this negative circumstance in that both polarities P15 and N15 now drive the compensation current ia simultaneously via the push-pull output stage G. The load Rb is connected between the two outputs of the push-pull output stage G, whereby one of the outputs, as described above, is previously led via this toroidal core RK as a compensation current ia via several windings to compensate for the magnetic field in the toroidal core RK. Driving the compensation current ia with both polarities P15 and N15 of the supply voltage simultaneously by a push-pull output stage G doubles the possible compensation current ia and thus also the primary current il that can be reproduced. The burden in the form of the electrical resistance Rb is no longer connected to ground, but is tapped "floating" 0 via a differential amplifier D.

The two inputs of the differential amplifier D are controlled by the two outputs of the push-pull output stage G. The differential amplifier D thus amplifies exactly the voltage that drops across the burden Rb. The burden voltage UB obtained at the output of the differential amplifier D is thus proportional to a measured primary current il, although larger primary currents il can now be converted. The differential amplifier D is preferably constructed using one or more commercially available operational amplifiers.

However, when the compensation current transformer of the type according to the invention is fully utilized, it may happen that the so-called "latch up" criterion is exceeded. When switching on, the positive and negative supply voltages P15 and P16 rise differently.

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N15 and uncontrolled overshoots in the control stage R can cause such a high compensation current ia that the probe system T attached to the magnetic ring core RK, in the case of the example a so-called T-field probe, goes into saturation and can therefore indicate an incorrect polarity. However, this reverses the control direction so that the evaluation electronics, e.g. within the control stage R, go into the "latch up" state.

For this reason, according to the invention, a "latch up" control LK is added, which excludes this state by implementing a "soft start". In addition, the symmetry and simultaneity of the positive and negative supply voltages P15 and N15 are monitored. The controller summation point of the evaluation electronics within the controller stage R is also monitored for irregular values. Such an irregular value is given, for example, when a larger difference occurs between the inverting and non-inverting input of the controller operational amplifier of the controller stage R, which indicates that the control loop is not normally closed, as is the case, for example, in a "latch up" state. For this reason, during the soft start and when deviations from the desired target states are detected, either one of the amplifier stages or both amplifier stages of the push-pull output stage G are switched to high impedance or to zero volts. The controller summation point from the controller stage R is fed to the input of the "latch up" control LK, which signals a deviation from the desired target states. Furthermore, the positive supply voltage P15 and the negative supply voltage N15 are fed to the "latch up" control LK in order to be able to carry out a soft start and to monitor the symmetry and simultaneity of the supply voltage. If there is a known deviation from one of the target states, the inverting amplifier stage I is then controlled by the output of the "latch up" control LK and, as described above, switched to high impedance or to zero volts. The "latch up" control can optionally

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LK can also limit the controller output of the controller stage R, such a possibility is indicated in the illustration according to FIG 1 by a broken connection.

The push-pull output stage and its cooling surfaces can be made significantly smaller, which saves space and costs and also makes it possible to use it in applications that were previously not possible due to space constraints. The entire electronics can also be easily integrated into a user-specified integrated circuit (ASIC). In addition, the power supply is less loaded and can be smaller, which also saves costs.

Claims (11)

GR 95 G 3905 11 Protection claims 1. Device for compensating current conversion, consisting of a magnetic field sensor (S), a subsequent regulator stage (R), two amplifier stages, which are designed as a push-pull output stage (G), which is in particular symmetrically fed (P15, N15), and a load in the form of a resistor (Rb), across which a voltage (UB) proportional to an input current (il) drops, characterized in that 1.1 Means are provided for clocking the amplifier stages, 1.2 the inductance of the compensation winding serves for smoothing. 2. Device according to claim 1, characterized in that 2.1 the clock frequency (f) is specified in the range between 100 kHz and 200 kHz. 0 3. Device according to claim 1 or 2, characterized in that 3.1 the clock frequency (f) can be derived from an oscillator (O) provided for exciting the magnetic field sensor (S).
25 4. Device according to one of the preceding claims, characterized in that 4.1 the clocking is pulse width modulatable. 0 5. Device according to claim 4, characterized in that 5.1 two comparators (Cl, C2) are provided for setting the pulse-pause ratio. 6. Device according to one of the preceding claims, characterized in that GR 95 G 3905 6.1 the load resistance (Rb) is designed as a floating load via a subsequent differential amplifier (D). 7. Device according to one of the preceding claims, characterized in that 7.1 the load in the form of the resistor (Rb) is connected between the outputs of the push-pull output stage (G), 7.2 the load in the form of resistance (Rb) between the both inputs of the differential amplifier (D) is connected. 8. Device according to one of the preceding claims, characterized in that 8.1 the regulator stage (R) and/or push-pull output stage (G) are controlled by a latch-up control (LK) which in particular monitors the symmetry of the positive and negative supply voltage (P15, N15) and the regulator sum point for irregular values. 9. Device according to one of the preceding claims, characterized in that 9.1 the primary current (il) is guided with a winding through a magnetic ring core (RK), in particular one with an air gap, 9.2 the compensation current (ia) is guided with several windings through the same magnetic toroidal core (RK). 10. Device according to one of the preceding claims, characterized in that 10.1 it can be integrated into a user-specified integrated circuit.