GB2052054A

GB2052054A - Means for Measuring Current, Temperature and/or Voltage in a Thyristor

Info

Publication number: GB2052054A
Application number: GB8017708A
Authority: GB
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1979-05-31
Filing date: 1980-05-30
Publication date: 1981-01-21
Also published as: FR2458076A1; SE7904751L; JPS55162073A; DE3019020A1

Abstract

A means for measuring the current, the temperature and/or the voltage in a thyristor (13) comprises at least one optical fibre (6) in optical contact with the thyristor, said optical fiber having the purpose of transmitting a light signal emitted from the thyristor and/or a light signal emitted to and through the thyristor, thus obtaining current-dependent, temperature-dependent and/or voltage-dependent signals which may constitute measurement values for the current, the temperature and/or the voltage occurring in the thyristor. In other embodiments for measuring the temperature of a thyristor, a semiconductor body (e.g. GaAs) having temperature-dependent optical properties is interposed between the thyristor and the end of the optical fibre. <IMAGE>

Description

SPECIFICATION Means for Measuring Current, Temperature-and/or Voltage in a Thyristor Technical Field This invention relates to a means for measuring the current, the temperature and/or the voltage occurring in a thyristor.

Voltage measurement of thyristors operating at a high potential nowadays requires an expensive and complicated electronic system capable of operating at a high potential and of emitting measurement values to earth potential. Current measurement requires current measurement devices, for example current transformers, which should also be capable of transmitting measurement values to earth potential from a high potential.

In the case of, for example, high-voltage direct current transmission systems, measurement devices of the above-mentioned kind involve heavy system costs. The present invention aims to provide a means for measuring the current, the voltage and/or the temperature occurring in a thyristor which is less expensive than hitherto known means of this nature.

Disclosure of Invention According to the invention, a means for measuring the current, the voltage and/or the temperature of a thyristor comprises at least one optical fiber arranged in optical contact with the thyristor for receiving and transmitting a light signal emitted from the thyristor and electrical circuit means for deriving from the transmitted light signal, at least one of (a) the current flowing in the thyristor, (b) the temperature of the thyristor and (c) the voltage across the thyristor.

As is weli-known, a thyristor is built up of a number of layers, P-base layers, N-base layers and Pemitter or anode emitter layers, and the anode end surface consists of an anode contact in the form of a metal layer. At the other end surface (the cathode) there is arranged a metal layer (the cathode contact) and a control contact, which is also in the form of a thin metal layer.

When the thyristor is in the on-state, electrons are injected from the cathode emitter and holes are injected from the anode emitter. A recombination between these electrons and holes is obtained in the body of the thyristor and gives rise to radiation emission as is described hereafter.

Brief Description of Drawings The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a section.through a thyristor, Figure 2 shows a coupling for temperature measurement, Figure 3 shows spectra for electro-luminescent light and the transmission spectrum of a filter, respectively, Figure 4 shows a semiconductor arranged between a fiber and a thyristor, Figure 5 shows a temperature measurement coupling, and Figures 6 and 7 show different circuits for current, voltage and temperature measurement.

Description of Preferred Embodiments The thyristor 13 shown in Figure 1 comprises a cathode emitter 1, a cathode contact 36, a Pbase layer 3, an N-base layer 4, a P-emitter or anode emitter layer 5, an anode emitter 2 and an anode contact 37. When the thyristor 1 3 is triggered, i.e. when it is in the on-state, there is a very strong injection of electrons from the cathode emitter 1 and of holes from the anode emitter 2 into the PNPregion 3-4-5. This leads to a very high concentration of electrons and holes arising in the PNPregion 3-4-5. As the electrons and holes recombine, radiation (electroluminescence) is emitted, the intensity of which is a measure of the current that passes through the thyristor.Some of this radiation, which is utilized in the present invention, is captured by an optical fiber 6 and is conveyed to an optoelectronic receiver unit, which measures the light intensity.

The light fiber 6 may rest directly against the end surface of the thyristor 13 in a hole provided for the fiber in the cathode contact 36, but the light fiber may instead be disposed adjacent to an end of the thyristor as indicated in dash-lines at 6'.

Measurement of off-state voltage and reverse blocking voltage is carried out as follows.

When the thyristor is in the off-state and the blocking state, the voltage appears across the PNjunctions 3-4 and 4--5, respectively. These PN-junctions are then subjected to dielectric fields of the order of magnitude 1 04 V/cm. Fields of this strength give rise to an energy state close to the energy band edges in the band gap of the semi-conductor (the Franz-Keldysh effect). This means that the absorption edge for light with a photon energy of approximately the same magnitude as the band gap of the semiconductor will increase. This absorption change in the thyristor 1 3 may be measured by feeding light with a photon energy he41 .1 eV (Figure 1) into the thyristor via the fiber 6.The light passes through the PNP-system 3-4-5 to a reflecting layer 7, for example an aluminium layer, where it is reflected back through the thyristor 1 3 and back into the fiber 6. The reflected light intensity in the fiber 6 is a measure of the absorption occurring in the PNP system, which, in turn, is a measure of the voltage applied across the off-state or blocking PN-junctlon(s).

The emitted light radiation from the thyristor 13 Is thus a measure of the current, and the refiected, partially absorbed light signal is a measure of the voltage. As will be shown hereinafter, the temperature in the thyristor 1 3 may also be measured.

Both the emitted light spectrum (he,) and the absorbed spectrum (he,) are dependent on the temperature of the semiconductor. It is therefore necessary to compensate for temperature variations in the semiconductor. One possibility of measuring the temperature is indicated in Figure 2. The optical fiber 6, which intercepts the emitted light when the thyristor is triggered or conducting, is divided between two fibers 8, 9 via a fiber branch. The two fibers 8 and 9 transmit light to photo-diodes 10 and 11, respectively. The photo-diode 11 is provided with a filter 12, but the photo-diode 10 has no such filter.The electrical output signals from the photo-diodes 10 and 11 are amplified in amplifiers 23 and 24, respectively, the output signals 1g and If of which are supplied to a quotient member 22. The output signal Is from the quotient member 22 becomes a measure of the temperature.

Figure 3 shows both the optical spectrum of the light g (hv, T) emitted from the thyristor and the transmission spectrum f (hop) of the filter 12. If the photo-diodes 1 0 and 11 have a spectral sensitivity distribution D (hv), the signals 19 and If may be as follows: 19=JD(hP) g(ho, T) d (hu)=G(T) (1) IrJrf(hP) D(hP) g(hv, T)d(hP) (2) Equation (2) may be rewritten as follows:: lrf(hP' (T))JD(hP) g(hv, T)d(hv)=f(hv'(T)) G(T) (3) where hv' is some photon energy within the integration interval. This photon energy becomes a function of the temperature T, since the spectrum g(hP, T) depends on T. By forming the quotient If/lg, as shown in Figure 2, the following is obtained: ís=lf/l=f(hP'(T)) (4) The signal 15 is therefore a measure of the temperature in the thyristor 13. The advantage of this method of determining the temperature is that it provides a measure of the actual temperature inside the body of the thyristor. The disadvantage is that the temperature can be measured only when the thyristor is triggered.This method also compensates for the effect of fiber bending of the fiber 6. Of course, current measurement may also take place according to Figure 2.

Another method for temperature measurement is shown in Figures 4 and 5. Figure 4 demonstrates the geometrical construction at the temperature measurement point. A semiconductor crystal 14 or other body of a temperature-sensitive material (material with a temperature-dependent absorption spectrum) is placed between the fiber 6 and the thyristor body 1 3. The semiconductor 14 has a band gap which is greater than the band gap of the semiconductor from which the thyristor is constructed. The normal thyristor material is silicon with the band gap of 1.1 eV, and so the semiconductor crystal 14 may suitably be gallium arsenide which has a band gap of 1.4 eV. Because of the difference in band gaps, the light emitted from the thyristor 13 with the photon energy hv1 will be completely transmitted through the semiconductor crystal 14.The surface 1 5 of the semiconductor crystal 14 is reflex treated with interference filters so that photons with the energy hPT near the band gap energy of the semiconductor crystal 14 are reflected, whereas photons with the energy hP, are completely transmitted. The absorption of this light in the semiconductor crystal 14 depends on the temperature because the band gap of the semiconductor crystal 14 is temperature-dependent. The reflected light with a photon energy of hPT is then signal-processed in the same way as in the earlier alternative for temperature measurement (see Figure 2).A circuit diagram is shown in Figure 5, in which a light-emitting diode (LED) 16 emits light of photon energy hPT and is modulated at a frequency of 4. The light from the LED 16 passes through the fiber 6, is reflected at the boundary surface 1 5 (see Figure 4) between the semiconductor crystal 14 and the thyristor 13, and is led back to the photodiodes 10 and 1 the diode 11 being provided with a filter 12. The signals are separated by means of demodulation. The continued signal processing is fully equivalent to the description with reference to Figures 2 and 3. The signal 1 corresponds to light emitted from the thyristor. The advantage of this measuring method is that the temperature of the thyristor 13 can be measured independently of its then existing operational mode.

The disadvantage is that it is the surface temperature of the thyristor which is measured, which temperature may have a time-delay with respect to the temperature inside the body of the thyristor in the event of rapid current and voltage changes. There are several alternative circuits that may be employed for temperature measurement.

Two alternative circuits according to the invention are shown in Figures 6 and 7. In Figure 6 the temperature dependence of the magnitudes to be measured is compensated by the emission method (current measurement), previously described in connection with Figure 2. Two LEDs 18 and 1 9 are used with different photon energies (hvR and hi'v, respectively, expressed in eV) of the emitted light.

Further, the diodes are modulated at two different frequencies fR and fvt respectively. The LED 1 8 emits a reference signal, which is reflected against the end 17 of the fiber 6 (see the encircled detail) close to the thyristor. The end 1 7 of the fiber 6 is coated with a reflex layer of interference type, which reflects light with a photon energy of hPR. The LED 19 has a photon energy of hi',=1 .1eV in the vicinity of the band gap for silicon This light passes straight through the fiber end 1 7 and the thyristor 13, and is reflected against the other side of the thyristor (see, for example, Figure 1). The absorption in the thyristor is a measure of the off-state or blocking voltage which is applied across it.When the thyristor is triggered, it luminesces with a photon energy of hP, and with an intensity which is a measure of the current through the thyristor. These three optical signals with photon energies of hPR, hi'v and hP, (reference, voltage and current, respectively) return to the fiber 6 and are led into a fiber 22 via a fiber branch and to photo-diodes 20 and 21, of which the photo-diode 21 is provided with an optical filter 12 with a characteristic according to Figure 3.After the photodiode 20, three electrical signals I,, 1R and 1I with the frequencies fV, fR and fi, respectively, are obtained, which are separated by band pass filtering, rectification and low pass filtering.The band pass filters are shown at 25 (for Iv with the frequency fV), at 26 (for 1R with the frequency fR) and at 27 (for 1I with the frequency f, and the rectifiers and the low pass filters are shown, respectively, at 28, 29 and0. The d.c. signals lv and 1I thus obtained are supplied to quotient members 31 and 32, respectively, where division is carried out with the reference signal 1R to compensate for the fiber bend of the fiber 6.Two signals S1 (VT) and S2 (IT) are then obtained, which depend on the voltage V and the current i of the thyristor, and also on its temperature T, To measure the temperature, the optical filter 12 in the diode 21 is utilized, the electrical signal after the diode 21 then being low pass filtered in order only to pass signals with frequencies < fi. The assumption is then that f t,, 4. After division by the rectified current signal II, a signal S3 (T) is obtained, which is a measure of the temperature of the thyristor according to the previous description regarding Figures 2 and 3.The signals S1, Sz and S3 are A/D-converted and are sent into a microprocessor 35 or some other electronic calculating unit which calculates the voltage, current and temperature values. After D/A conversion, the signals V, I and T are obtained, said signals being proportional to the voltage, current and temperature of the thyristor.

Figure 7 shows an alternative circuit, in which the temperature is measured by measuring the absorption in a GaAs crystal 14, which is located between the fiber 6 and the thyristor 13 (see the encircled detail showing the reflex layer 1 5). This means that an additional LED with a photon energy of hsT and a modulating frequency 4 has to be introduced. Furthermore, after the photo-diode 21 the signal must be band-pass filtered at 4 (see 36), and the signal thus obtained is divided by the reference signal 1R in a quotient member 37. Otherwise the principle is the same as in the circuit shown in Figure 6.

For voltage measurement, different fibers may be used for the input signal and the output signal, and these fibers should be positioned on opposite sides of the thyristor.

Claims

1. Means for measuring the current, the temperature and/or the voltage in a thyristor, comprising at least one optical fiber arranged in optical contact with the thyristor for receiving and transmitting a light signal emitted from the thyristor and electrical circuit means for deriving from the transmitted light signal, at least one of (a) the current flowing in the thyristor, (b) the temperature of the thyristor and (c) the voltage across the thyristor.

2. Means according to claim 1 in which the optical fiber is arranged to pass light into the thyristor and to receive light from the thyristor.

3. Means according to claim 2, in which a reflecting layer Is applied on one side of the thyristor, opposite to the point where the fiber is connected, said reflecting layer being located and adapted to reflect light coming from the fiber back through an intermediate portion of the thyristor.

4. Means according to claim 1 or 2, in which at least one optical fiber for incoming light is in optical contact with one side of the thyristor, and at least one other optical fiber is in optical contact with the opposite side of the thyristor to transmit a light signal that has passed through the thyristor.

5. Means according to claim 1 or claim 2, in which several optical fibers are connected to the thyristor in order to make it possible to perform measurements at different points of the thyristor.

6. Means according to claim 1, in which the optical fibre is disposed to monitor that portion of the thyristor where the current density is a maximum.

7. Means according to claim 1, in which the optical fiber is connected in parallel with the boundary layer surfaces of the thyristor.

8. Means according to claim 1, in which a body of a material with a temperature-dependent absorption spectrum is arranged between the end of the optical fiber and the thyristor.

9. Means according to claim 1 or claim 2, in which a light signal emitted from the thyristor via an optical fiber is adapted to be supplied to at least two different photon-sensitive receivers of different sensitivity spectra, the output signals of the receivers being supplied to a calculating member in order to obtain a signal dependent on the temperature of the thyristor.

10. Means according to claim 8, in which a frequency modulated light signal is fed to the said body of temperature-sensitive material, which signal is reflected at a boundary layer between the said body and the thyristor, the light signal re-reflected through the said body then being dependent on the temperature of the said body, and thus that part of the thyristor which is adjacent to the said body.

11. Means according to claim 10, in which output signals from two light-emitting diodes with different photon energies are adapted to be emitted to the light fibre, the diodes being adapted to be modulated at different frequencies, or to be switched in at different times.

12. Means according to claim 11, in which the end of the fiber adjacent to the thyristor is coated with a reflecting layer of interference type, whidh selectively reflects the light signal from only one diode.

1 3. Means according to claim 12, in which the light output signal from the thyristor and the reflecting layer at the fiber end are supplied to two photo-diodes, one via a filter with a specific transmission spectrum, and the output signal from the diode without a filter is adapted to be demultiplexed into three signals, corresponding to the light sent through the thyristor, the light reflected at the fiber end, and the light emitted from the thyristor.

14. Means according to claim 13, in which the demultiplexed signals are adapted to be supplied to two quotient members, one for the two modulating-frequency dependent signals for the purpose of obtaining a signal dependent on the voltage and temperature of the thyristor, and one for one of these signals and the operating frequency dependent signal, for the purpose of obtaining a signal dependent on the current and temperature of the thyristor.

15. Means according to claim 13, in which the output signal from the photo-diode provided with a filter is adapted to be supplied, via band pass filtering means and rectifying means, to a quotient member together with the previously mentioned operating-dependent output signal for the purpose of obtaining a measure of the temperature of the thyristor.

16. Means according to claim 14 or 15, in which a body of a temperature-sensitive material is arranged between the fiber end and the thyristor, said body having a reflecting layer of interference type at its boundary with the thyristor.

1 7. Means according to claim 13, in which the rectified output signals are adapted to be supplied to a calculating member in order to calculate the current, voltage and temperature values.

18. Thyristor measuring means substantially as hereinbefore described with reference to, and as illustrated in, Figure 2, 5, 6, or 7 of the accompanying drawings.