WO2000079675A1

WO2000079675A1 - Method for identifying a load that can be connected according to demand to a power inverter, and a corresponding load identification system

Info

Publication number: WO2000079675A1
Application number: PCT/AT2000/000161
Authority: WO
Inventors: Christoph Panhuber; Christian Angerer
Original assignee: Fronius Schweissmaschinen Produktion Gmbh & Co. Kg
Priority date: 1999-06-16
Filing date: 2000-06-09
Publication date: 2000-12-28
Also published as: AT409803B; ATA105699A; AU5509100A

Abstract

The invention relates to a method for identifying a load (3) that can be connected according to demand to a power inverter (1), and a corresponding load identification system (18). According to the invention, the power inverter (1) is supplied with power, especially with a direct voltage, from a power source (2), especially from a battery (4). The supplied direct voltage is converted by the power inverter (1) via a bridge circuit (12) and a transformer (11) into an alternating voltage for supplying the load (3) that can be connected to the secondary side (14) of the transformer (11). The load identification system (18) detects or determines a voltage fluctuation occurring at the input terminals (5, 6) of the power inverter (1) or detects or determines a strain on the power source (2). At at least two established points in time or measuring points, an actual value of the input voltage is determined and a differential value is subsequently formed which is compared with a predetermined reference value. The power inverter (1) is activated or deactivated when the differential value exceeds or falls short of the reference value.

Description

Method for recognizing a load that can be connected to an inverter as required and corresponding load detection system

The invention relates to a method for recognizing a load connected to an inverter and to a load detection system for an inverter, in particular an island inverter, as described in claims 1 and 16

Load detection systems are already known in which a load is connected to an inverter on the secondary side of a transformer. In these, however, the load detection takes place on the secondary side of the transformer in the form of a simple one

Current measurement is disadvantageous here because, due to the galvanic isolation by the transformer, the control signals for a control device have to be transferred in a galvanically isolated manner to the Pπmar side of the transformer for control or regulation at great expense, and thus considerable costs arise or due to the high electronic complexity of such inverters are very sensitive

The invention has for its object to provide a method and a load detection system in which a load can be detected without additional effort for galvanic isolation

This object of the invention is achieved by the measures in the characterizing part of claim 1. It is advantageous here that load detection can be carried out on the pπmar side of the transformer. This also means that no galvanically isolated feedback of the signals is required, and it is also possible that even low loads, such as a 15 watt energy-saving lamp, can be recognized by the evaluation circuit without great effort, since the sensitivity for load detection can be set or changed in a simple form by changing the threshold values or reference values or the percentage deviation.Another advantage is that with a loads of this type can also be used to detect loads which cause only a slight or no increase in the amplitude of the load curve of the energy source, but only cause a phase shift. This means that non-detection of low loads is ruled out. A major advantage also harbors then that an energy-saving operation of the inverter is achieved, since it is only activated for a short time for load detection in idle mode and thus the idle losses without connected load are reduced or kept very small. Energy-saving operation of the inverter is thus achieved, so that the operating time - it is significantly increased for such an island inverter, which is operated with a battery. In addition, the idle losses are reduced by the primary-side load detection, since a simple circuit structure with few components and thus with low idle losses has been created.

Further advantageous measures are described in claims 2 to 15. The resulting advantages can be found in the description.

The invention further comprises a load detection system as described in claim 16.

The object of the invention is also achieved independently by the features in the characterizing part of claim 16. It is advantageous here that such a load detection system can be used for any inverter known from the prior art, or that existing inverters can be converted or retrofitted.

Further advantageous embodiments are described in claims 17 to 24. The resulting advantages can be found in the description.

The invention is subsequently described in more detail by means of exemplary embodiments.

Show it:

1 shows a circuit diagram of an inverter with the load detection system according to the invention, in a simplified, schematic representation;

FIG. 2 shows a characteristic curve of the output voltage of the inverter according to FIG. 1 in a simplified, schematic representation;

3 shows a characteristic curve of the output current of the inverter according to FIG. 1 in a simplified, schematic representation;

4 shows a characteristic curve of the input signals of the inverter according to FIG. 1 in a simplified, schematic representation; 5 shows a further exemplary embodiment of a circuit diagram of an inverter with the load detection system according to the invention, in a simplified, schematic representation,

6 shows an exemplary embodiment of the load detection system for an inverter according to FIG. 1 or 5, in a simplified, schematic illustration,

7 shows a characteristic curve of the output voltage of the inverter according to FIG. 1 or 5, in a simplified, schematic representation,

8 shows a characteristic curve of the input signals of the load detection system according to FIG. 6 in a simplified, schematic representation

In the introduction, it is stated that the same parts of the individual exemplary embodiments are provided with the same reference numerals. The position information given in the individual exemplary embodiments is to be applied accordingly to the new position in the event of a change in position

1 to 4 show an exemplary embodiment of an inverter 1, in particular an island inverter, with a load detection system and voltage and current signals that run over time

The inverter 1 has the task of supplying a direct voltage supplied by an energy source 2, for example a direct voltage in the amount of 12V = or 24V =, to an alternating voltage for supplying a load 3, in particular an alternating voltage load, with an effective value of approximately 230V to convert Since such a supply of the load 3 with an alternating voltage of, for example, 230V from the energy source 2, in particular a battery 4 with a direct voltage of, for example, 12V =, is already known from the prior art, the functional principle of the inverter 1, in particular on the voltage increase, not discussed in more detail

In the exemplary embodiment shown schematically, the inverter 1 is connected to the energy source 2, in particular the battery 4, via input terminals 5, 6 and supply lines 7, 8, an internal resistance 9 of the battery 4 and a line resistance 10 being shown schematically in the supply lines 7, 8 of the supply lines 7, 8 are shown In the case of the inverter 1, only the most important components are shown for the sake of simplicity. The inverter 1 comprises, for the transmission of energy, a transformer 1 1 via which the secondary load 3 is galvanically separated from the primary circuit, and a bridge circuit 12, in particular a full bridge, with the center of the both bridge branches a Pπmar side 1 of the transformer 1 1 is connected

Series to the primary winding or Pπmarseite 13 of the transformer 1 1 a choke arranged On a secondary winding or secondary side 14 of the transformer 1 1, the load 3 can be connected via output terminals 15, 16, with an activated power supply to the load at the output terminals 15, 16 3 with an AC voltage of, for example, 230V. The control of the

The inverter 1, in particular the bridge circuit 12, is undertaken by a control device 17, in particular a microprocessor control, the switching elements of the bridge circuit 12 being schematically connected to the control device 17. The further components required for such a system or for such an inverter 1, such as bypass capacitors, short circuit detection devices, etc. have not been shown

A load detection system 18 according to the invention is now arranged between the input terminals 5, 6, that is to say in the energy supply circuit of the pπmar side 13 of the transformer 11. The load detection system 18 is formed by a measuring circuit 19 and an evaluation circuit 20. It is also possible for the evaluation circuit 20 is integrated directly in the control device 17. The function of the load detection system 18 is subsequently described with the aid of the curve diagrams shown in FIGS. 2 to 4. For this purpose, the diagram in FIG. 2 shows a sinusoidal output voltage 21 present at the output terminals 15, 16 and in FIG 15, 16 flowing sinusoidal output current 22 in the no-load condition, that is, without a connected load 3, is shown in FIG. 4, an input voltage 23 or the voltage at the battery 4 is shown, which is detected at the input terminals 5, 6 by the measuring circuit 19

Through such a construction of an island inverter, in particular the inverter

1, a load detection, that is to say a distinction between the idle state without a connected load 3 and a loaded state with a connected load 3 on the pπmar side 1 of the transformer 11 is realized. This ensures that - not as is known from the prior art - one load detection carried out on the secondary side 14 of the transformer 11. for example by measuring the current at the output terminals 15, 16, is realized, but that this takes place directly on the primary side 13. The system known from the prior art has the major disadvantage that, similarly to the galvanic isolation by the transformer 11, the measurement signals for the current measurement for the control device 7 are likewise galvanically isolated on the primary side 13 of the transformer 11, with great effort must be transmitted to the control device 17, and thus considerable costs arise or such inverters are very sensitive due to the high electronic complexity.

If the inverter 1 is put into operation, that is to say the energy source 2, in particular the battery 4, via the correspondingly controlled switching elements of the full bridge with the

Inverter 1 connected, so when a load 3 is connected, the load 3 is appropriately supplied with an AC voltage. The control device 17 controls the bridge circuit 12 in such a way that an opposite pole voltage is successively applied to the primary winding of the transformer 11 by opening or closing the switching elements in opposite directions. This results in an energy transfer to the secondary side 14 of the transformer 11 and the load 3 can thus be supplied with energy. The principle of operation will not be discussed in detail, since any tax or Control method can be used for an inverter 1 and / or for the bridge circuit 12.

According to the invention, it is now provided that a load detection for the load 3 connected to the secondary side 14 is carried out on the primary side of the transformer 11, i.e. that the load detection system 18 checks whether a load 3 is connected to the output terminals 15, 16 or not. It is possible that the load 3 is formed, for example, by an incandescent lamp, energy-saving lamp or another AC voltage consumer and is either connected directly to the output terminals 15, 16 or with the interposition of a switching device, such as a light switch, optionally by a user to the inverter 1 can be switched.

In order to be able to carry out a corresponding primary-side load detection, the control device 17 periodically activates the inverter 1, in particular the bridge circuit 12, that is to say that after the activation of the inverter 1, a load detection is carried out first, so that it can be determined whether a corresponding current flow in the output circuit, that is to say via the output terminals 15, 16, takes place or not. If no load 3 was identified, the bridge circuit 12 and the other components of the Switch 1 is deactivated again and a new load detection is carried out after a predetermined, presettable period of time has elapsed. The time intervals for the periodic activation of the bridge circuit 12 and the other components (not shown) can be preset by the user or these are preset by the manufacturer and are preferably in such a range that the user has a delay in

Connection of the load 3 to the inverter 1 is not noticed. Such a periodic, short-term activation can achieve considerable energy savings, where a longer operating time with the same battery 4 is possible

If the control device 17 and the load detection system 18 carry out a load detection, the activation of the inverter 1, in particular the bridge circuit 12, results in a current and voltage flow from the positive potential of the energy source 2 in alternating directions via the polar side 13 of the transformer 11 and the choke to the negative potential of the energy source 2, the corresponding sinusoidal output voltage 21 and the corresponding output current 22 also being produced

The measuring circuit 19 constantly or continuously monitors the input voltage 23 at the input terminals 5, 6 or the battery voltage, and when the bridge circuit 12 is not activated, a no-load voltage 24, as shown in a stippled manner, is detected without significant interference signals or voltage drops due to an inductive one Loading the inverter 1 or the transformer 11 or a capacitive loading indicated by dashed lines by a capacitor results in a corresponding voltage drop at the energy source 2 when the bridge circuit 12 is activated. Furthermore, the inductive or capacitive loading causes a phase shift between the voltage and the current at the output caused by approximately 90 °, as at times 25 to 29 between the

Output voltage and the output current can be seen. Accordingly, a current zero crossing occurs simultaneously at the maximum voltage amplitude

The additional ohmic internal resistance 9 of the battery 4 and the line resistance 10 of the supply lines 7, 8 on the pπmar side 13 of the transformer 11 also result in an ohmic voltage drop on the battery 4 as a result of a load on the battery 4 by the inverter 1 possible that a series resistor is arranged in the primary supply circuit of the transformer 11, whereby a defined minimum load can be achieved. In particular, a sinusoidal change in the terminal voltage or a sinusoidal output curve, in particular an open circuit voltage voltage 30, on the battery 4 or on the input terminals 5, 6 and measured, which has a double frequency to the generated output voltage 21, for example of 100 Hz. This sine wave fluctuating battery voltage is detected by the measuring circuit 19 at the input terminals 5, 6 and forwarded to the evaluation circuit 20 For this purpose, it is possible for the measuring circuit 12 to be formed, for example, by a resistance bridge

The load-related voltage drop can be seen in FIG. 4 on the basis of the open-circuit voltage 30 shown in full lines compared to the constant open-circuit voltage 24. The change from the open-circuit voltage 24 to the fluctuating open-circuit voltage 30 enables the

Evaluation circuit 20 recognize that a load detection is to be carried out. Evaluation circuit 20 now evaluates the voltage fluctuation which occurs at energy source 2 at input terminals 5, 6 of inverter 11 in such a way that at least two voltage values at at least two different times 25 to 29 or measurement - Points, in particular at times 26 and 27, are determined, whereupon a comparison with stored reference values or setpoints is carried out. In this case, times 26 and 27 for determining the voltage values are matched to twice the frequency for output voltage 21, thereby achieving that due to the open circuit voltage 30 formed at twice the frequency of the output voltage 21, it is always ensured that two different voltage values can be determined and thus a step evaluation, that is to say a minimum / maximum evaluation of the voltage load, can be carried out as a matter of course ch, it is possible for the input voltage, in particular the voltage values of the battery, to be recorded at a plurality of times 25 to 29

In particular, the measurement frequency between successive measurements for determining the voltage drop is four times the frequency of the output voltage 21 of the inverter 1 Successive voltage measurements are carried out within a period of time, which amounts to a quarter of the period of the output voltage 21 to be able to The input voltage actual values, in particular the voltage values, can be determined for comparison with the reference values in such a way that a difference value, in particular a differential voltage 31, of the determined voltage values is calculated at the specified measuring points or at times 26, 27, which is then subsequently is compared by the evaluation circuit 20 with a fixed reference value. If this result now exceeds a predetermined threshold value or reference value, the evaluation circuit 20 recognizes that a load 3 is connected to the inverter 1 and activates the inverter 1 permanently. Of course, it is possible that the evaluation is carried out in the form of percentage deviations from a reference value, that is to say that if the predetermined percentage deviation in the voltage dips on the battery 4 is exceeded or reached, or if the upper and / or lower values are exceeded or undershot a load 3 is detected in the upper threshold value.

It is now assumed that no consumer or no load 3 is connected to the inverter 1, as is also indicated by the designation open circuit voltage 30, so that the

Evaluation circuit 20 no deviation or only a slight deviation, which occurs, for example, due to a change in resistance of the battery 4 or from leakage losses of the transformer 11, is present and there is therefore no exceeding of the defined threshold value or the percentage deviation. The evaluation circuit 20 then sends a signal to the control device 17, with which it is informed that no load 3 is connected to the output terminals 15, 16. The control device 17 then deactivates the bridge circuit 20, as a result of which an unnecessary load on the battery 4 is avoided and considerable energy savings are thus achieved.

If a user activates a consumer or a load 3 is applied to the output terminals 15,

16 connected, after the standby phase of the inverter 1 has ended, a new load detection takes place, in which this load 3 is now recognized by the evaluation circuit 20. This is done in such a way that the load detection cycle is carried out as previously described.

Due to the current flow that is now formed via the load 3, a greater current load on the battery 4 is caused in the overall system of the inverter 1. This additional current flow occurs because each consumer or load 3 has an ohmic or inductive or capacitive resistance or alternating current resistance, which leads to a corresponding current flow, the current flow compared to the idle state The connection of the load 3 to the output terminals also leads to an increased voltage drop at the energy source 2, which means that a higher load on the energy source 2, in particular the battery 4, is recognized, since there is a greater sinusoidal drop in the input voltage 23 at the input terminals 5, 6 These dips are illustrated in FIG. 4 in the form of a load voltage 32. The evaluation circuit 20 in turn evaluates the voltage values that occur at times 26, 27 and in turn forms a differential voltage 33, in particular a differential value, which is compared with the nominal or reference or maximum value

By increasing the total load and the associated increase in the difference value, this difference value is exceeded via a defined reference value or threshold value or a predetermined percentage maximum deviation, as a result of which the evaluation circuit 20 detects the load 3 at the output of the inverter 1. This evaluation result is transmitted to the Forwarded control device 17, whereupon the control device 17 sets a so-called continuous operation of the inverter 1, ie that all components, in particular the bridge circuit 12, remain activated and thus an energy supply to the load 3 is ensured

Such a method now makes it possible for load detection to be carried out on the polar side 13 of the transformer 11. This means that there is no need for any galvanically isolated feedback of the signals or the measurement signals to the control device 17, and it is also possible that Low loads 3, such as a 15 watt energy-saving lamp, can be recognized by the evaluation circuit 20, since the sensitivity of the load detection is caused by changing the threshold values or the percentage, maximum

Deviation can be set or changed

Furthermore, it has been shown in an advantageous manner that for the commissioning of the inverter 1 or after longer use of the same energy source 2, in particular the battery 4, a calibration cycle for determining the total resistance and thus the reference value or

Target values or threshold values can be carried out. This adjustment cycle is explained in more detail

So that a deactivation of the consumer or a separation of the load 3 is also recognized, the evaluation circuit 20 continuously monitors the input voltage 23 carried out, ie. that, for example, a certain evaluation of the differential voltage 33. in particular the differential value, and a subsequent comparison with the target value is carried out at certain preset time intervals, so that when the reference value or the percentage deviation is undershot, it can be recognized that the load 3 has been deactivated and continuous operation is thus canceled by control device 17 by means of a signal from evaluation circuit 20.

In the exemplary embodiment shown in FIG. 1, a so-called low-frequency inverter 1 with a frequency of the output voltage of, for example, 50 Hz has been described.

5 shows a further exemplary embodiment of an inverter 1, in which a high-frequency inverter 1 is now shown, the same reference numerals being used for the same parts or components. The function for the primary-side load detection corresponds to the functional description for FIGS. 1 to 4. The load detection system 18 is in turn connected to the input terminals 5, 6 of the inverter 1.

The illustrated high-frequency inverter 1 is an inverter 1 known from the prior art, as a result of which it works on the principle of operation

Inverter 1 is not discussed in detail. Of course, it is possible that any high-frequency or low-frequency inverter 1 can be equipped with the primary-side load detection system 18 according to the invention.

This inverter 1 is in turn assigned an energy source 2, in particular a battery 4, which is now connected to a high-frequency transformer 11, for example for a frequency between 20 to 40 kHz, and a switching element 34. The switching element 34 chops the DC voltage supplied into a high-frequency voltage, which is transmitted to the secondary side 14 via the transformer 11. This high-frequency voltage is subsequently rectified and fed to a bridge circuit 12, in particular a full bridge. The switching element 34 is activated in such a way that the voltage in the intermediate circuit, that is to say at the input of the bridge circuit 12, is kept as constant as possible.

The voltage supplied by the bridge circuit 12 is opened in cycles and Closing two switching elements to the load 3 connected in the middle of the left and right bridge branch via the output terminals 15, 16 in the form of an alternating voltage. It is possible for appropriate chokes to be connected upstream between the two output terminals 15 Component, in particular a capacitor 35, switched, whereby an approximately sinusoidal

AC voltage at the output or to the load 3 can be applied or transferred. This capacitive component, in particular the capacitor 35, also produces a phase shift, preferably of approximately 90 °, between the output current and the output voltage, so that the corresponding control and / or control method, as described in FIGS. 1 to 4, can be used for the load detection system 18 on the pπmar side

FIGS. 6 to 8 show a further exemplary embodiment of a load-side load detection according to the invention, the same reference symbols being used for the same parts or components

In this case, only an equivalent circuit diagram in the form of a block diagram of the load detection system 18 is shown in FIG. 6, which is connected to the input terminals 5, 6 of an inverter 1. FIG. 7 shows a signal of an output voltage 21 for a load 3 and in FIG. 8 is a signal course of a measurement signal, which at the input of the evaluation circuit

20 of the load detection system 18 occurs

The load detection system 18 in turn has the measuring circuit 19, which is now connected to an amplifier 37, in particular a reversing amplifier with a high-pass filter. The amplifier 37 has the task of evaluating the input signal evaluated by the measuring circuit 19, in particular the input voltage, as described above Figures in order to amplify a fixed value and at the same time to filter out the DC voltage component by means of the high-pass filter. This ensures that the evaluation circuit 20 only has to evaluate the sinusoidal load curve - according to FIG. 8

For the load detection on the Pπmar side 13 of the inverter 1, it is in turn possible that, as already in the previously described FIGS. 1 to 5, at at least two measuring points, which are fixed by times 25 to 29 fixed relative to the output voltage 21 and in particular by the Times 26, 27 are formed, the input signal is measured or the input voltage actual values are determined, and the amplifier 37 amplifies the value circuit 20 are supplied. The evaluation circuit 20 forms a difference value of the two measured voltage values and compares this with stored reference values or a percentage deviation from a specified value or a reference value and thereby determines whether a load 3 is connected to the output of the inverter 1. In particular, if the comparison values or the reference value are exceeded, a load 3 is connected and operation of the inverter 1 is initiated or, if the result is the opposite, active operation is ended.

Furthermore, a further control or regulating method for the load detection system 18 will now be described, with the corresponding signal curves being entered in FIG. 8 for this purpose. This control or regulating method is preferably suitable for recognizing small loads 3, such as a so-called "fluorescent lamp".

For this purpose, a low-pass filter, which is not shown, is arranged after the amplifier 37 or directly into the amplifier 37. The low-pass filter causes a specific phase shift of the measured no-load voltage 30 or the voltage taken off at the input terminals 5, 6 relative to the output voltage 21. The measuring points, in particular the times 26, 27 for determining the actual values of the voltage or the actual input voltage values of the However, amplified input signals are retained and are matched to the output voltage 21, namely to its extreme values zero and maximum. It is thereby achieved that a lower differential voltage 31 is set, so that a substantial increase in the sensitivity of the load detection is achieved.

If a load 3 is connected to the inverter 1, a further phase shift occurs with a low current consumption of the load 3, a load voltage 32 having full lines being entered in FIG. 8 for this purpose. This load voltage 32 causes a hardly measurable voltage load on the energy source 2, but a phase shift to the open circuit voltage 30. This preferably has an effect on loads 3 which represent small ohmic loads 3 or have a rectifier in their circuit.

For the evaluation, a difference voltage 33 is again determined by the evaluation device 20 at the fixed times 26, 27, which are synchronized or coordinated with the output voltage 21. As can clearly be seen from FIG. 8, the determined differential voltage 33 of the load voltage 32 at times 26, 27 is significantly larger than the differential voltage 31 of the open circuit voltage 30, so that by comparing the load detection is possible for the two successively measured differential voltages 31, 33. For this purpose, a percentage deviation or a reference value comparison can again be carried out by the evaluation circuit 20. However, a comparison of two successive differential values or differential voltages 3 1 and 33 is preferably carried out in this control or regulating method, so that load detection can be determined on the basis of a corresponding change in the differential value or the differential voltage.

The main advantage of such a control or regulating method lies in the fact that loads 3 can also be recognized which cause only a slight or no increase in the amplitude of the load curve of the energy source 2, but only cause a phase shift. This prevents a non-detection of low loads 3. Of course, it is possible that the described control or regulating method according to FIGS. 1 to 8 can be combined with one another.

In order to ensure that a load 3 on the secondary side 14 of a transformer 11 is detected on the primary side, an adjustment method can be carried out before the inverter 1 is started up or after the inverter 1 has been in operation for a long time or the battery 4 has been in use for a longer period of time. The purpose of this adjustment method is to compare the individual setpoints or reference values for comparison with the measured or determined values

Adapt actual values for the evaluation circuit 20, for which purpose the inverter 1 is operated in idle mode, that is to say without a load 3 connected to the secondary side 14 of the transformer 11.

The advantage of the adjustment method is that consideration is given to the individual states of the components, in particular the internal resistance 9 of the battery 4 and the line resistance 10 of the supply lines 7, 8, as well as other ohmic resistances acting on the load detection system 18, and thus reliable detection is possible with small loads 3. It is because of the nature of things that certain ohmic resistances, such as the internal resistance 9 of the battery 4, become longer

Change the use, so that again a reliable load detection is possible by a new adjustment of the inverter 1 to the new conditions.

For this purpose, for example, the user can start the adjustment process at any time by activating a switching element implemented on the housing of the inverter 1 or will at this adjustment procedure is carried out automatically when the inverter 1 is started up for the first time. It only has to be ensured that no load 3 is connected to inverter 1 during the adjustment process.

In the adjustment process, the control device 17 or the evaluation circuit 20 determines an open-circuit value, in particular the differential voltage 31, by starting an interrogation cycle or by a measurement process for recognizing a load 3, that is to say by activating the bridge circuit 12. This or its value is then stored in a non-volatile memory, so that the evaluation circuit 20 can at any time use this value for a comparison with a determined input voltage actual value, that is to say that this idle value is now stored as a reference value or setpoint and accordingly the methods used for the comparison with an actual value, the calculation is carried out on the basis of this determined target value. In the previously described FIGS. 1 to 8, there are different methods for comparing the evaluation circuit 20, such as a threshold value comparison, a percentage deviation, a phase shift and a simple target / actual value.

Comparison, has been described, it being mentioned in principle that these methods are based on a corresponding starting value, which is now formed by this idle value determined.

This adjustment method also has the advantage that the most varied energy sources

2, in particular batteries 4 with different internal resistances 9 can be taken into account. A factory setting of the reference value or setpoint value or the switch-on threshold is not sensible because of different internal resistances of the batteries 4. However, it is possible that 4 different reference values are set by the manufacturer for the most diverse batteries and that the user has to set the appropriate battery type when starting up the inverter 1 and then the evaluation circuit 20 can access the correct reference value.

It is also possible that the evaluation circuit 20 always stores the last determined value, in particular the differential voltage 31, 33, whereupon the evaluation circuit 20 uses this value for the comparison in the case of a new detection cycle, so that if there is a corresponding deviation, a load 3 can be recognized. To do this, however, it is necessary for the inverter 1 to be activated in idle mode or for the adjustment process to be carried out at the beginning in order to obtain a defined output value. It can be stated that the relationship between the differential voltage 31 in no-load operation and the differential voltage 33 with a load 3 is independent of the connected energy source 2, in particular the battery 4, and thus a primary-side load detection can also be carried out without these components. However, it has been found that the inclusion of the ohmic resistances of the energy source 2 and the supply lines 7, 8 enables a more precise evaluation to be carried out, that is to say that loads 3 with a low electrical power requirement can thereby also be reliably identified. The adjustment method described above can be used for each of the previously described embodiments.

In conclusion, it should be pointed out that in the exemplary embodiments described above, the individual parts or components or assemblies are shown schematically or in simplified form. Furthermore, individual features of the combinations of features of the individual exemplary embodiments described above can form independent solutions according to the invention in conjunction with other individual features from other exemplary embodiments.

Above all, the individual in FIGS. 1, 2, 3, 4; 5; 6, 7, 8 shown form the subject of independent solutions according to the invention. The tasks and solutions according to the invention in this regard can be found in the detailed descriptions of these figures.

REFERENCE NUMBERS

Inverter Energy source Load Battery Input terminal Input terminal Supply line Supply line Internal resistance Line resistance Transformer Bridge circuit Primary side Secondary side Output terminal Output terminal Control device Load detection system Measuring circuit Evaluation circuit Output voltage Output voltage Input voltage Quiescent voltage Point in time Point in time Point in time Open circuit voltage Differential voltage Load voltage Differential voltage Switching element Capacitor Measuring signal Amplifier

Claims

Patent claims

1. Method for detecting a load (3) that can be connected to an inverter (1) as required, the inverter (1) being supplied with energy, in particular with a DC voltage, by an energy source (2), in particular a battery (4) and the inverter (1) transforms the supplied DC voltage into an AC voltage via a bridge circuit (12) and a transformer (11) to supply the load (3) that can be connected to the secondary side (14) of the transformer (11), characterized in that a load detection system (18) generates a voltage fluctuation or load on the input terminals (5, 6) of the inverter (1)

Energy source (2) is detected or ascertained, an actual value of the input voltage (23) being ascertained at at least two fixed times (25-29) or measuring points and a difference value being subsequently formed, which is compared with a predetermined reference value, with at Exceeding or falling below the reference value of the inverter (1) is activated or deactivated.

2. The method according to claim 1, characterized in that the control or regulation of the inverter (1) by a control device (17), in particular a microprocessor control, is carried out.

3. The method according to claim 1 or 2, characterized in that the inverter (1), in particular the bridge circuit (12). is periodically activated by the control device (17) for load detection.

4. The method according to one or more of the preceding claims, characterized in that the time intervals for the trial, short-term activation of the inverter (1) are preset by a user or specified by the manufacturer.

5. The method according to one or more of the preceding claims, characterized in that a measuring circuit (19) continuously or continuously monitors the input voltage (23), with a non-activated inverter (1) or inactive bridge circuit (12) a quiescent voltage (24) is detected at the energy source (2) without significant interference signals or voltage dips.

6. The method according to one or more of the preceding claims, characterized in that by an inductive load and / or a capacitive load on the transformer (1 1), for example by an output filter, with an activated inverter (1) or active bridge circuit (12) without connected load (3) a relatively low load on the energy source (2) is determined and these load values are preferably used to determine the reference value.

7. The method according to one or more of the preceding claims, characterized in that a phase shift, for example by 90 °, is caused by the inductive or capacitive load between the output voltage (21, 22) and the output current of the inverter (1).

8. The method according to one or more of the preceding claims, characterized in that an ohmic voltage drop occurs at the internal resistance of the battery (4) by a load on the inverter (1), which causes a sine-like change in the

Terminal voltage of the battery (4) generated, which has a double to the output voltage (21, 22) of the inverter (1), for example of 100 Hz, which is detected by the measuring circuit (19) at the input terminals (5, 6) and is forwarded to an evaluation circuit (20).

9. The method according to one or more of the preceding claims, characterized in that the measuring circuit (19) is formed by a resistance bridge.

10. The method according to one or more of the preceding claims, characterized in that the evaluation circuit (20) performs a step evaluation, that is to say a minimum / maximum evaluation of the voltage dips and / or the energy source load.

1 1. The method according to one or more of the preceding claims, characterized in that the evaluation circuit (20) has a difference value, in particular a

Differential voltage (31, 33), which is calculated or ascertained at the specified measuring points or at specific times (25 - 29) synchronized or coordinated with the output voltage (21, 22), which differential value or which differential voltage (31 . 33) is then compared by the evaluation circuit (20) with a defined reference value.

12. The method according to one or more of the preceding claims, characterized in that a specific phase shift of the input voltage (23) measured at the input terminals (5, 6) to the output voltage (21, 22) is formed by a low-pass filter.

13. The method according to one or more of the preceding claims, characterized in that the evaluation circuit (20) in turn at the fixed times (25-29) or measuring points which are synchronized or coordinated with the output voltage (21, 22) , a differential voltage (31, 33) under load (3) and / or a differential voltage (31, 33) is determined in idle.

14. The method according to one or more of the preceding claims, characterized in that the evaluation circuit (20) stores the idle differential voltage (31, 33) and then uses it for comparison with a newly determined differential voltage (31, 33) .

15. The method according to one or more of the preceding claims, characterized in that before the commissioning of the inverter (1) or after a long period of operation or a longer period of use of the inverter (1), an adjustment method is carried out.

16. Load detection system (18) for an inverter (1), in particular an island inverter, the inverter (1) being connectable to an energy source (2), in particular a battery (4), and the inverter (1) for galvanically isolating one Load (3) and for transforming a supplied voltage comprises a transformer (1 1), the load (3) or an electrical consumer being assignable to a secondary side of the transformer, characterized in that the load detection system (18) for detecting an at the The secondary side (14) of the transformer (1 1), which can be connected to the load (3), is assigned to the primary side (13) or the primary circuit of the transformer (1 1) and an evaluation or detection can be carried out in accordance with the method according to one or more of claims 1 to 15 is.

17. Load detection system according to claim 16, characterized in that the load detection system (18) with the energy supply circuit of the primary side (13) of the transformer (1 1). especially with the input terminals (5. 6) of the inverter (1), is bound.

18. Load detection system according to claim 16 or 17, characterized in that the load detection system (18) is formed by a measuring circuit (19) and an evaluation circuit (20).

19. Load detection system according to one or more of the preceding claims, characterized in that the inverter (1) has a bridge circuit (12), in particular a full bridge.

20. Load detection system according to one or more of the preceding claims, characterized in that the primary side (13) of the transformer (1 1) is arranged in a center of the bridge circuit (12).

21. Load detection system according to one or more of the preceding claims, characterized in that the transformer (1 1) is formed by a low-frequency or a high-frequency transformer (1 1).

22. Load detection system according to one or more of the preceding claims, characterized in that the evaluation circuit (20) is integrated directly into a control device (17) responsible for controlling or regulating the inverter (1).

23. Load detection system according to one or more of the preceding claims, characterized in that the load detection system (18) between the measuring circuit (19) and the evaluation circuit (20) comprises an amplifier (37), in particular an inverting amplifier with a high-pass filter.

24. Load detection system according to one or more of the preceding claims, characterized in that a low-pass filter is arranged between the amplifier (37) or the measuring circuit (19) and the evaluation circuit (20).