Heating Control System and Method for Switching on a Heating Load

Abstract

A heating control system and method for switching on a heating load, wherein the heating load is controllable via forward-phase control, and wherein, at a particular instant in time, the forward-phase control has a corresponding phase control angle, where the heating load is switched on via a specifiable initial phase control angle and an ascertained effective current and a definable switch-on current curve are taken into account in order to determine the subsequent phase control angles such that an efficient cold start with any heating loads can be performed.

Claims

1. A method for switching on a heating load, the heating load being controllable via forward-phase control having a corresponding phase control angle, the method comprising: switching on the heating load via a specifiable initial phase control angle; and determining subsequent phase control angles taking into account an ascertained effective current and a definable switch-on current curve.

2. The method as claimed in claim 1, wherein the heating load exhibits positive temperature coefficient (PTC) thermistor properties.

3. The method as claimed in claim 1, wherein the initial phase control angle is at least 90.

4. The method as claimed in claim 3, wherein the initial phase control angle is at least 120.

5. The method as claimed in claim 2, wherein the initial phase control angle is at least 90.

6. The method as claimed in claim 5, wherein the initial phase control angle is at least 120.

7. The method as claimed in claim 1, wherein the phase control angles that follow the initial phase control angle are at least one of (i) calculated from the ascertained effective current and (ii) determined from the ascertained effective current.

8. The method as claimed in claim 1, wherein the initial specifiable phase control angle is selected according to a temperature of the heating load.

9. The method as claimed in claim 1, wherein the definable switch-on current curve does not exceed a characteristic curve of a protective device.

10. The method as claimed in claim 1, wherein a distance between the definable switch-on current curve and a characteristic curve of a protective device is not less than a definable minimum distance.

11. The method as claimed in claim 1, wherein the switch-on is concluded when a phase control angle of 50 or less has been reached.

12. The method as claimed in claim 1, wherein the switch-on is concluded when a phase control angle has been reached which is less than an angle defined by a controller for operation after a switch-on process.

13. The method as claimed in claim 1, wherein the heating load is controlled via half wave control after the switch-on.

14. The method as claimed in claim 1, wherein the method is repeated when a definable cooling time of the heating load is exceeded.

15. The method as claimed in claim 1, wherein the method is repeated whenever the heating load is switched on.

16. A heating control system, comprising: a power section configured to control a heating load via forward-phase control having phase control angles; and a controller which controls the power section such that the heating load is switched on utilizing a specifiable initial phase control angle; wherein subsequent phase control angles are determined taking into account an ascertained effective current and a definable switch-on current curve.

17. The heating control system as claimed in claim 16 wherein the heating control system is configured to: switch on the heating load via a specifiable initial phase control angle; and determine the subsequent phase control angles taking into account the ascertained effective current and the definable switch-on current curve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention is described and explained in greater detail below with reference to the exemplary embodiments shown in the figures, in which:

[0025] FIG. 1 is a schematic circuit diagram of a power channel;

[0026] FIG. 2 is a graphical plot showing the relationship of phase control angle and effective value of the current over a half-wave;

[0027] FIG. 3 is a graphical plot showing a trip curve of a protective device and a switch-on current curve of the present method in accordance with the invention; and

[0028] FIG. 4 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0029] FIG. 1 shows a schematic circuit diagram of a power channel as might be used with the method in accordance with the invention. The central component is a switch T1, which here is in the form of a triac by way of example; thyristors or other power semiconductors are also conceivable. In addition, FIG. 1 shows a switch T2, which here is in the form of an opto-triac and is employed for galvanic isolation of the power channel from a controller CTRL. FIG. 1 also shows the input voltage UIN, which can be measured by a first voltage measuring device MU1, and thereafter a protective device FUSE, which protects the power channel. The current flowing through the first switch T1 is measured in the current measuring device MI. An output of the power channel OUT is equipped with a second voltage measuring device MU2, with a heating load LOAD connected to the output OUT of the power channel. It is particularly advantageous that the voltage measuring devices MU1, MU2 are not needed for the method in accordance with the invention. These have been shown for the sake of completeness and can be used, for example, for additional plausibility checking of the method and for other functionalities.

[0030] When an appropriate signal comes from the controller CTRL, the opto-triac T2 fires and the triac T1 is thereby likewise triggered. The input voltage UIN is then applied to the load OUT, and a current flows that depends on the resistance of the load LOAD at that time. Here, current measuring device MI can be in the form of a Hall sensor and provide measured current values. The first voltage measuring device MU1 is used for measuring the input voltage UIN, while the second voltage measuring device MU2 is used for measuring the voltage across the load. The controller CTRL can perform forward-phase control or reverse-phase control, and also other known techniques, such as PWM or variations. The protective device FUSE may be a fuse, for example, which has a suitable fuse characteristic curve, as shown in FIG. 3. Manufacturers of protective devices often specify time/current curves, as they are called, from which it is possible to read off how long a certain effective current value can flow on average before the protective device trips.

[0031] FIG. 2 shows the relationship of phase control angle and effective value I.sub.EFF of the current over a half-wave HW. In the top graph, a normalized power in percent % is plotted on the vertical axis; both graphs span a half period of 0 to 180. The amplitude AMP is plotted in the bottom graph and extends from 0 to 1, again in normalized form here. The top graph shows the effective current I.sub.EFF that arises and the corresponding power P. The bottom graph shows a corresponding half-wave, for instance the voltage half-wave HW. A phase control angle of 120 is selected by way of example. Assuming that the current over time follows an ideal sinusoid, then an effective value of approximately 44% of the effective value I.sub.EFF is obtained for the selected firing angle.

[0032] FIG. 3 uses a segment of a trip curve FUSE.sub.max of a protective device FUSE to illustrate how converging as quickly as possible on a defined switch-on current curve I.sub.Start, and following this curve, is meant to be achieved via phase control angles determined by the method.

[0033] The trip curve shown is a curve that plots an effective current I.sub.EFF against the melting time T.sub.MELT. Here, the switch-on current curve I.sub.Start exhibits a defined distance DIST from the maximum current/time curve FUSE.sub.max. The distance DIST could be reduced further here by a parallel shift to achieve an even faster switch-on process. The consequence of this, however, would be a reduced buffer and the design of the system would need to take this into account accordingly. The initial firing angle .sub.INIT results in a low initial effective current I.sub.EFF, and therefore it is possible to determine directly after the initial firing what subsequent load is permitted. The current is brought onto the defined switch-on current curve already using the first phase control angle 1. The further phase control angles 2 to 5 are used to continue to follow accordingly the switch-on current curve I.sub.Start and to allow a more efficient and faster start-up process without endangering the protective device FUSE or the power channel or even the entire heating system. The effective current I.sub.EFF converges successively on the switch-on current curve I.sub.Start with each of the further phase control angles 2 to 5. As a result of the PTC-thermistor characteristic, the resistance of the heating load falls with increasing temperature, and the phase control angles 2 to 5 can be adjusted accordingly.

[0034] To summarize, the invention relates to a heating control system and method for switching on a heating load LOAD, wherein the heating load LOAD can be controlled by means of forward-phase control, and wherein the forward-phase control at a particular instant has a corresponding phase control angle 1, . . . , n, where in order to allow an efficient cold start with any heating loads, the following steps are performed, i.e., switching on the heating load LOAD via a specifiable initial phase control angle INIT, and determining the subsequent phase control angles 1, . . . , n taking into account an ascertained effective current I.sub.EFF and a definable switch-on current curve I.sub.Start.

[0035] FIG. 4 is a flowchart of the method for switching on a heating load LOAD, where the heating load LOAD is controllable via forward-phase control having a corresponding phase control angle 1, . . . , n. The method comprises switching on the heating load LOAD via a specifiable initial phase control angle INIT, as indicated in step 410. Next, subsequent phase control angles 1, . . . , n are determined taking into account an ascertained effective current I.sub.EFF and a definable switch-on current curve I.sub.Start, as indicated in step 420.

[0036] Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.