EP1154202B2 - Control device for a burner - Google Patents

Abstract

The regulating device (15) for a burner has an ionization electrode (16) in the flame area of the burner influencing the fuel and air feed amounts dependent upon a positioning signal (18). Connected beyond the ionization electrode is an ionization evaluator (14) which produces an ionization signal (13). In a control unit (23), in which characteristic data is stored for determining a first condition of the positioning member (17), is produced time wise a first control signal (24). A regulator (26) produces the positioning signal at least time wise dependent upon the ionization signal and likewise dependent upon the first control signal (24).

Description

The invention relates to a control device for a burner, which burner comprises a arranged in the flame region of the burner ionization electrode, and an actuator, which affects the fuel supply amount or the air supply amount in response to a control signal.

Ionization electrodes have long been used for flame monitoring in burners. In general, however, the ratio of the amount of air to the amount of fuel, often called lambda, matched with each power demand either by a controller or by a scheme with sensors on each other. In general, lambda should be slightly above the stoichiometric value 1 for each power demand, for example, 1.3.

Air-controlled burners react, unlike controlled burners, to external influences which change the combustion. They therefore have a higher efficiency and thus a higher efficiency and lower pollutant emissions and thus a lower environmental impact. However, the sensors required for this, often gas sensors, in particular oxygen sensors, or temperature sensors, are expensive, unreliable, in need of care and / or have a short service life for this purpose.

For many years, therefore, burner manufacturers and control equipment manufacturers have tried to use the existing ionization electrode not only for flame monitoring, but also as a burner control sensor. DE-A1-3937290 describes a test setup for controlling the gas-air ratio, in which the ionization electrode is fed with a DC voltage. This principle is not very suitable for mass production. It is not possible to monitor the flame with the same ionization electrode, since only the rectifier characteristic of the flame may be used for this purpose.

Published a few years ago IT 95U000566 and EP-A1-909922 which describe control devices for gas burners. In a simplified representation, it describes how the actuator is controlled on the basis of a stored characteristic in the case of dynamically rapid changes in the gas or air volume flow. In contrast, with slow changes in the gas or air volume flow, a fine adjustment takes place on the basis of the control with the ionization signal as the measured variable.

Rapid changes in fuel supply or air supply typically result from sudden changes in power demand. In addition, changes in the air number and thus changes in the gas or air volume flow may be caused by changes in the fuel composition, changes in air pressure, gas pressure changes, temperature changes, soiling and wear of mechanical torch parts, etc.

The stored characteristic in the control devices IT 95U000566 and EP-A1-909922 sets at each air pressure of the blower, and thus at each requested power, a control signal, which corresponds to a nearly desired level of the actuator for the gas valve. Also, an alternative control device is described, according to which the air volume flow is adapted to the gas volume flow, and the characteristic curve approximately determines the desired fan speed as a function of the manipulated variable of the gas valve.

A burner-specific characteristic curve is obtained in that the burner is operated under varying load with changing actuator levels, with additional sensors measuring emission values and efficiency and thus determining the desired manipulated variables.

Air-controlled burners have advantages over devices that are controlled by means of characteristic curves. At constant power, changes in temperature, fuel pressure, air pressure, fuel composition, wear and soiling of mechanical parts, etc. drift away from the set operating point.

Because of this, the control devices cause IT 95U000566 and EP-A1-909922 When rapid power changes occur, a control based on the stored characteristic curve compensates for their imperfection by first shifting the last state of the control signal to a new value at a constant distance along the characteristic curve.

About the same time, the owner of EP-A2-806610 Control devices developed which have also stored a characteristic for the control signal. The characteristic also basically serves to control the actuating signal during rapid power changes, while the ionization current still lags behind the facts.

In DE-A-19831648 It shows a method for the functional adaptation of a control electronics of a gas heater on the type-specific properties, which should proceed largely independently. With the control electronics, the combustion air volume flow and the fuel gas volume flow can be controlled in dependence on a combustion-dependent ionization signal. For adaptation, the control electronics controls before the actual burner operation firing operations with different air flow rates and stores the resulting characteristics for future burner operation.

Some of the above-mentioned prior art control devices are on the market, but have significant disadvantages. You still need additional sensors and / or keep the air-gas ratio with dynamic changes in performance little stable. Market acceptance is accordingly low.

It has been found that a significant improvement in controlling a burner via the ionization electrode in the inventive measures of claim 1 lies.

Surprisingly, these measures, which are easy to implement, provide the long-desired jump in control quality. The structure of a control device according to the invention requires little resources, such as electronic components and computer capacity of a microprocessor. For the unique initial setting of a control device to a certain type of burner instead of previously one, now two or more burner-specific characteristics must be determined.

Practice has shown that the second control signal contributes above average to specify the control of the control signal.

By the way, the control device can be constructed in such a way that, on detection of suitable conditions, it itself carries out a setting procedure for the acquisition of new characteristic data. Thus, occasional or periodic recalibration occurs to compensate for any creeping changes in the control system, such as wear or fouling of the ionization electrode. Another possibility is that the control characteristics are automatically determined, even for gases that are not detected by the preset characteristics.

The characteristic data can be designed, for example, as the constants in a polynomial winding up to the third order. The function approximately represented by the polynomial winding determines a relationship between an input parameter and the actuating signal.

The input parameter for the cams is initially the requested power, either in the form of a manipulated variable or a measured variable that corresponds to the power, for example, the fan speed. Of course, other sizes can be used as input to the control characteristics, z. B. Temperature signals of all kinds such as burner temperature, flow and return temperature, etc. Further examples include a pressure difference reading for determining the gas or air flow, a gas or air flow meter, or directly the drive signal for operating a gas valve or an oil pump.

Advantageously, the first and second behaviors of the actuator depend on input parameters that are the same size. The measure of the requested power, or another physical quantity, can be supplied to the control unit by means of a single input parameter, such as the manipulated variable of the fan speed, or by input parameters of different types, such as manipulated variable and measured variable of the fan beam.

But this is not necessary. If, in particular, the control device has further measured values available during operation, from which it can determine, for example, the current energy content or the current pressure of the supplied fuel directly or indirectly, then the second input parameter can even represent another variable.

Often burners are equipped with a temperature sensor for the boiler temperature. A change in the energy content of the fuel supplied has a change in boiler temperature. In such a burner, for example, the manipulated variable of the fan speed is the first input parameter, and the temporal change of the boiler temperature of the second. There are characteristics have been stored, which determine a first desired behavior of the actuator with different benefits, but fixed energy content of the fuel and other fixed influences. Also, characteristics have been stored which determine a second behavior with different energy contents and this time fixed power.

In this scenario, the controller determines any changes in the actual energy content of the supplied fuel based on boiler temperature changes that do not correspond to the time history of the fan speed and generates a corrected power-dependent control curve using the characteristics for the second behavior and the ionization signal. In the case of a dynamic power change, the control signal will follow the thus corrected control curve, for example at a constant distance.

Burners of various designs are possible, for example premixed gas burners or atmospheric burners with and without auxiliary blower. In atmospheric burners without auxiliary fan, the air flow z. B. via a damper o. Ä. Are controlled.

The controller generates the control signal at least temporarily by processing the control signals and determines the processing at least temporarily as a function of the ionization signal.

This includes some variants. For example, the control unit generates no control signals in a quasi-stable state. The controller then makes a pure control of the ionization signal. However, as soon as a rapid state change occurs, the controller switches to the fast-response and accurate control by processing the control signals. The manner in which the control signals are processed has previously been fixed by the ionization signal and remains the same throughout the control period. The control is only replaced by a control when the state has calmed down and the Ionisationssignal has lagged the current state. According to Alternatively, however, the control signals are generated permanently, and both the control signals and the ionization signal continuously contribute to the control signal. Mixed variants are also possible.

In any case, the controller is at least temporarily weighted and added to the control signals and that the controller determines the weighting at least temporarily as a function of the ionization signal.

In an advantageous embodiment of the invention, the controller attenuates rapid fluctuations of the ionization signal in comparison to slow fluctuations before the processing of the control signals. In particular, the controller is provided with a low-pass filter for the ionization signal or for a processed signal generated by processing, or with an integration unit for the Ionisationss or for a generated by processing sequence signal.

The processing of the control signals is adjusted by these measures only with a certain delay and / or smoothing of the ionization, so that the anyway too slow ionization signal course after a sudden change in state does not interfere with the control signal. Only when the situation has calmed down will the ionization signal slowly act on the processing of the control signals to provide a fine tuning.

In a further embodiment of the invention, characteristic data for determining a behavior of the ionization signal are stored in the control unit, the control unit generates at least temporarily a setpoint signal and the controller generates the control signal at least temporarily in response to the setpoint signal.

By means of these measures, the regulator device, or its regulator program, can be designed simply and achieve great reliability. Optionally, the controller itself occasionally or regularly calibrates these characteristics.

In the mentioned embodiment of the invention, the controller is advantageously equipped with a comparison unit which at least at times subtracts the setpoint signal or a sequence signal generated by processing from the ionization signal. In this embodiment, the controller may generate the actuating signal in such a way that the ionization signal is regulated to the desired value signal. By the above-mentioned integrating unit, this difference can be regulated to zero.

Another embodiment of the invention relates to the stored characteristic data. Advantageously, the first behavior of the actuator during a burner operation has been determined with a first fuel, and the second behavior of the actuator during a burner operation with a different in energy content second fuel, especially if the specific energy content of a fuel at least 5% higher than that of another Fuel is.

It has been shown that the characteristic curves are so different from each other from this limit value that they give the control device substantial additional information compared to a control device with only one stored characteristic curve. This substantially increases the extent of some advantages that the invention entails.

In this embodiment, the characteristics for determining the two behavior of the actuator have resulted from measurements. Alternatively, however, only the characteristics for the first behavior of the actuator are determined based on measurement results. The characteristics for the second behavior are then calculated from these. This is only possible if a person skilled in the art has suitable knowledge of the behavior of the actuator under the different circumstances.

In a variant of the above-mentioned embodiment, the characteristic data for the second behavior are determined by means of burner-specific measurements based on expert knowledge of the fuel mixtures fed in practice.

The setting of a control device to a certain type of burner thus advantageously takes place in that two or more burner-specific characteristics during operation with different fuels, such as gas mixtures in different proportions, are determined.

The invention also relates to a method for adjusting an inventive control device. According to this method, a burner is first equipped with an inventive control device and with additional sensors for determining the quality of the combustion. Then one operates the burner with a first fuel with a certain energy content at different power levels, each with different actuator levels, wherein one determines a desired actuator state from the sensor results for each power value. From the desired actuator levels characteristics are determined to determine the first behavior of the actuator. Thereafter, the burner is operated with a second fuel having a different energy content at different power levels, each with different actuator levels, from the sensor results for each power value determining a desired actuator level, and now determining characteristics from the desired actuator levels to determine the second behavior of the actuator , Optionally, repeat these steps for a third or even more fuel. Finally, the identified characteristic data are stored in one or more control devices. As described above, it brings advantages that the specific energy content of one fuel is at least 5% higher than that of another fuel.

• Figur 1 zeigt ein Blockschaltbild eines Ionisationsauswerters in einer Regeleinrichtung gemäss der Erfindung,
• Figur 2 zeigt ein Blockschaltbild einer Regeleinrichtung gemäss der Erfindung, und
• Figur 3 zeigt das Stellsignal einer Regeleinrichtung gemäss der Erfindung.

Alternatively, one operates the burner with a fuel supply at a first pressure at different power levels, each with different actuator levels, wherein a desired actuator level is determined from the sensor results for each power value. From the desired actuator levels characteristics are determined to determine the first behavior of the actuator. Thereafter, the burner is operated with a fuel supply at a different second pressure at different power levels, each with different actuator levels, and a desired actuator level determined from the sensor results for each power value. Characteristics for determining the second behavior of the actuator are now determined from the desired actuator levels. Finally, you save the identified characteristics in a control device. The inventive effect is particularly pronounced when the differences in the fuel supply pressures exceed 9%, that is, when a fuel supply pressure is at least 9% higher than another.

• FIG. 1 shows a block diagram of an ionization evaluator in a control device according to the invention,
• FIG. 2 shows a block diagram of a control device according to the invention, and
• FIG. 3 shows the control signal of a control device according to the invention.

Fig. 1 schematically shows the principle of operation of an Ionisationsauswerters 14 in a control device according to the invention. In an equivalent circuit, the flame 1 is represented by a diode 1a and a resistor 1b. About L and N, an AC voltage of, for example, 230V is applied. When a flame 1 is present, a larger current flows through the blocking capacitor 3 in the positive half wave than in the negative half wave because of the flame diode 1a. As a result, a positive DC voltage U _{B is formed} on the blocking capacitor 3 between L and a resistor 2 mounted for the purpose of contact protection.

By a decoupling resistor 4, therefore, a direct current flows from N to the blocking capacitor 3. The amount of direct current depends on U _B and thus directly from the flame resistance 1b. The flame resistance 1b also influences the alternating current through the decoupling resistor 4, but to varying degrees compared to the direct current. Through the resistor 4 thus flows a direct current and an alternating current as described above.

The resistor 4 is now followed by a high pass 5 and a low pass 6. Through the high-pass 5, the alternating current is filtered out and the DC component blocked. The low-pass filter is used to filter out the dc voltage component which is dependent on the flame resistance 1b and essentially blocks the alternating current. In an amplifier 7, the alternating current flowing from the high-pass filter 5 is amplified and a reference voltage U _{Ref is} added. In an amplifier 8, the direct current flowing from the high-pass filter 6 is amplified with possibly small alternating current components and the reference voltage U _{Ref is} added.

The reference voltage U _Ref can be chosen arbitrarily, for example U _Ref = 0, but it is preferably chosen so that the amplifiers and comparators only need one supply.

At a comparator 9, the alternating voltage emerging from the amplifier 7 and the DC voltage emerging from the amplifier 8 are compared with one another and a pulse width modulated (PWM) signal is generated. If the amplitude of the mains voltage changes, the AC voltage and the DC voltage change in the same ratio, the PWM signal does not change. The signal swing of the PWM signal can be adjusted by means of the amplifiers 7 and 8 in a wide range between τ = 0 and τ = 50% duty cycle.

The DC voltage component U _- is compared in a comparator 10 with the reference voltage U _Ref . If a flame is present, the DC component is greater than the reference voltage (U ₌ > U _Ref ) and the comparator output of the comparator 10 switches to 0. If no flame is present, the DC component is approximately equal to the reference voltage (U ₌ ≈ U _Ref ). Because of the, the DC voltage component superimposed, low AC voltage component that the low-pass filter 6 does not filter out, the DC component briefly falls short of the reference voltage and appear at the comparator output of the comparator 10 pulses. These pulses are applied to a retriggerable monoflop 11.

The monoflop 11 is triggered so that the pulse train output from the comparator 10 comes faster than the pulse duration of the monoflop. If a flame is present, the monoflop will not be triggered and the output will always show a 0. The retriggerable monoflop 11 thus forms a "missing pulse detector" converts the dynamic on / off signal into a static on / off signal.

Both signals, the PWM signal and the flame signal can now be further processed separately or linked by means of an OR gate 12. As an output of the OR gate 12, if the flame is present, a PWM signal is shown whose duty cycle is a measure of the flame resistance 1b. This ionization signal 13 is the in FIG. 2 shown controller 26 supplied. If no flame is present, the output of the OR element is permanently at 1. The ionization signal 13 can be transmitted via an optocoupler, not shown, in order to achieve a protective separation between the mains side and the protective low voltage side.

FIG. 2 shows a block diagram of a control device 15 according to the invention. The ionization electrode 16 protrudes into the flame 1. The gas valve 17 is controlled by the control signal 18 in a direct or indirect manner, for example via a motor. Eventually, a mechanical pressure regulator is interposed.

An air blower 19 is driven to a speed which is used here as an input parameter. The speed corresponds to a power demand 22. The speed signal 20 is fed via a filter 21 to the control unit 23, which has been designed as a program part for execution in a microprocessor. There characteristic data are stored, which define the characteristics of a first and a second control signal 24 and 25. The controller 26 weights and adds the two control signals and thus determines the actuating signal 18. This processing of the control signals depends on the ionization signal 13.

The ionization signal 13 is first smoothed by the controller 26 by means of a low pass filter 27 to suppress glitches and flicker. In a comparison unit 28, a setpoint signal 30 generated by the control unit 23 and routed via a correction unit 29 is subtracted. From the sequence signal of this processing of the ionization signal, an internal control value x is determined by a proportional controller 31 and a parallel integrating unit 32, which weights the two control signals 24 and 25 and thus fine-tunes the actuating signal 18.

The control value x may alternatively be generated by a PID controller or a state controller from the sequence signal.

FIG. 3 shows how the control signal 18 of a control device 15 according to the invention depending on the speed signal 20 runs. The characteristics of the control signals 24 and 25 each relate to a fuel gas with a fairly deep, correspondingly high caloric value.

In a quasi-stable state in which the fuel gas has an average combustion value and the combustion values deviate from the characteristic curves due to other circumstances, the control device 15 regulates the control signal via the weighting of the control signals 24 and 25 to an almost optimal for the air-gas ratio Value 33. This fine control corresponds to a vertical movement of the control signal value in the FIG. 3 ,

Now finds a step-like increase in the power demand 22 instead, and a corresponding change in the speed signal 20, then the weighting of the two control signals remains barely touched for the time being. However, the control signals 24 and 25 themselves each rise rapidly with the speed change to their corresponding higher values along the characteristics, and the control signal 18 also increases rapidly to the value 34. This controlled value 34 of the control signal is already very accurate, that is, is close to an optimum value for the air-gas ratio. Once the ionization signal 13 has re-recorded to the new state, typically after a few seconds, it controls the weighting of the control signals 24 and 25 again fine. It moves in the FIG. 3 the control signal 18 vertical to a value 35.

Claims (13)

1. A regulating device (15) for a burner, comprising an ionisation electrode (16) arranged in the flame region of the burner, a setting member (17) which influences the feed amount of fuel or the feed amount of air in dependence on a setting signal (18), equipped with an ionisation evaluating device (14) which is connected downstream of the ionisation electrode (16) and which produces an ionisation signal (13), a control unit (23) in which characteristic data for determining a first mode of behaviour of the setting member (17) are stored and which at least at times produces a first control signal (24), and a regulator (26) which produces the setting signal (18) at least at times in dependence on the ionisation signal (13) and at least at times in dependence on the first control signal (24), and that in the control unit (23) are stored characteristic data for determining a second mode of behaviour of the setting member (17), the control unit (23) produces at least at times a second control signal (25), and the regulator (26) produces the setting signal (18) at least at times in dependence on the second control signal (25), characterised in that the regulator (26) produces the setting signal (18) at least in part by processing of the control signals (24, 25), arid the regulator (26) determines the processing at least at times in dependence on the ionisation signal (13) and the regulator (26) at least at times weights and adds up the control signals (24, 25) and the regulator (26) determines the weighting at least at times in dependence on the ionisation signal (13).
2. A regulating device according to claim 1 characterised in that prior to processing of the control signals (24, 25) the regulator (26) damps rapid fluctuations in the ionisation signal (13) in comparison with slow fluctuations.
3. A regulating device according to claim 2 characterised in that the regulator (26) is equipped with a low pass filter (27) for the ionisation signal (13) or for a sequence signal produced by processing.
4. A regulating device according to claim 3 characterised in that the regulator (26) is equipped with an integrating unit (32) for the ionisation signal (13) or for a sequence signal produced by processing.
5. A regulating device according to each of the preceding claims characterised in that characteristic data for determining a mode of behaviour of the ionisation signal (13) are also stored in the control unit (23), the control unit (23) produces at least at times a reference value signal (30), and the regulator (26) produces the setting signal (18) at least at times in dependence on the reference value signal (30).
6. A regulating device according to claim 5 characterised in that the regulator (26) is equipped with a comparison unit which at least at times subtracts the reference value signal (30) or a sequence signal produced by processing from the ionisation signal (13) or from a sequence signal produced by processing.
7. A regulating device according to claim 5 or claim 6 characterised in that the regulator (26) so produces the setting signal (18) that the ionisation signal (13) is regulated to the reference value signal (30).
8. A regulating device according to one of the preceding claims characterised in that the first mode of behaviour of the setting member (17) has been determined during a burner operation with a first fuel and, the second mode of behaviour of the setting member (17) has been determined during a burner operation with a second fuel which differs in respect of the energy content.
9. A regulating device according to claim 8 characterised in that the specific energy content of a fuel is at least 5% higher than that of another fuel.
10. A method of setting a regulating device for burners according to one of the preceding claims characterised in that a burner is equipped with a regulating device (15) and with additional sensors for establishing the quality of combustion, the burner is operated with a first fuel with a certain energy content at different output values with respective different setting member statuses, wherein a desired setting member status is established from the sensor results for each output value, characteristic data for determining the first mode of behaviour of the setting member (17) are established from the desired setting member statuses, the burner is operated with a second fuel with a different energy content at different output values with respective different setting member statuses, wherein a desired setting member status is established from the sensor results for each output value, characteristic data for determining the second mode of behaviour of the setting member (17) are established from the desired setting member statuses, and the established characteristic data are stored in a regulating device(15).
11. A method of setting regulating devices for burners according to claim 10 characterised in that the specific energy content of a fuel is at least 5% higher than that of another fuel.
12. A method of setting a regulating device for burners according to claim 10 or claim 11 characterised in that the burner is operated with a fuel feed under a first pressure at different output values with respective different setting member statuses, wherein a desired setting member status is established from the sensor results for each output value, characteristic data for determining the first mode of behaviour of the setting member (17) are established from the desired setting member statuses, the burner is operated with a fuel feed under a different second pressure at different output values with respective different setting member statuses, wherein a desired setting member status is established from the sensor results for each output value, characteristic data for determining the second mode of behaviour of the setting member (17) are established from the desired setting member statuses, and the established characteristic data are stored in a regulating device (15).
13. A method of setting a regulating device for burners according to claim 12 characterised in that a fuel feed pressure is at least 9% higher than another.

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