Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
  • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
  • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
  • H02M7/5387—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
  • H02M7/53871—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
  • H02M7/53873—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with digital control

Definitions

• the present invention relates to a method for converting a first alternating current signal into a second alternating current signal, in which, starting from the first alternating current signal, switches are activated taking into account specifications and measured values determined during the conversion, and a converter for carrying out this method .
• I ⁇ s is known to convert a first AC signal into a second alternating current signal by switches are controlled in a suitable manner. This conversion is carried out by converters in which the ratio between the frequency of the first AC signal and the frequency of the second AC signal is given by the construction of the converter.
• the object of the present invention is to remedy the aforementioned deficiency in the prior art.
• 1 is a block diagram of the converter, which is used to carry out the present method
• FIG. 4 shows the principle of reaching a signal with a periodically variable amplitude
• FIG. 5 shows the behavior of the converter when it is overloaded.
• the converter shown in Fig. 1 has a rectifier 1 and an inverter 2, wherein the inverter 2 is connected to the output of the rectifier 1.
• the converter also has a control device 3, which controls the mode of operation of the inverter 2 in accordance with fixed and adjustable specifications and instantaneous values or measured values determined during the operation of the converter.
• a consumer 4 which in the present case is an asynchronous motor, is connected to the output of the inverter 2.
• the converter is fed from a single-phase network via a rectifier bridge 6.
• a DC voltage is available at the output terminals of this rectifier bridge 6, the positive pole + Uo being on the output terminal of the bridge 6 and the negative pole -Uo of the DC voltage on the output terminal shown below.
• a smoothing capacitor / is also connected to the output terminals + Uo and -Uo of the rectifier bridge 6.
• the inverter 2 which in the present case is designed to supply a three-phase AC signal, contains a pair of switches 11, 12 for each phase of the output signal; 13, 14; and 15, 16, the switches of the respective pair being connected in series. MOS-FET serve as switches. Since in the example shown a three-phase AC signal is should be sufficient, the inverter 2 contains three pairs of switches 11 and 12, 13 and 14 and 15 and 16 and the ends of these serial combinations of switches 11 to 16 are connected to the output terminals + Uo and -Uo of the rectifier bridge 6. The respective output conductor 17, 10 and 19 of the inverter 2 is between the switches of the corresponding pair of switches 11, 12; 13.14; 15.16 connected.
• the control unit 3 contains a computer 5 which receives the signals which are decisive for the generation of the second alternating current signal, processes them and forms signals for controlling the inverter 2 therefrom.
• the switches 11 to 16 shown are n-channel MOS-FET.
• the drain electrode 8 of the first transistor 11 is connected to the positive terminal + Uo of the rectifier bridge 6.
• the source electrode 9 of this switch 11 is connected to the drain electrode 8 of the second transistor 12 which is connected in series with this first switch 11, the output conductor 17 of this pair of switches 11, 12 also being connected here.
• the source electrode 9 of the second switch 12 is connected to the negative terminal -Uo of the rectifier bridge 6.
• the gate electrodes 10 of these switches 11 and 12 are connected via units 25 to the respective output of the computer 5.
• the other pairs of switches 13 and 14 or 15 and 16 connected to one another and connected to the computer 5.
• the remaining output conductors 18 and 19 are connected at the node between transistors of these further pairs of switches.
• means 20 for adjusting the frequency of the output signal, means 21 for adjusting the amplitude of the output signal, means 22 for adjusting the direction of rotation of the motor 4, means 23 for program selection and for selecting setting values and Mit ⁇ are to the inputs of the computer 5 in the example shown tel 24 connected to choose options.
• Monitoring signals for example when the converter is overloaded, pass from a monitoring unit 26 in the rectifier circuit 1 to further inputs of the computer 5.
• Means 27 for the optical display of the set and / or measured values are connected to at least one further output of the computer 5.
• the single-phase or multi-phase AC voltage is converted by the rectifier bridge 6 into a DC voltage which is available at the terminals + Uo and -Uo.
• current is fed into the output conductors 17 to 19 are passed through one of these switches of the respective switch pair, which has the effect of signals with corresponding polarity in the output conductors 17 to 19 and thus also an alternating voltage at the output of the inverter 2.
• FIG. 2 shows the principle of how a signal 31 with a constant amplitude is generated on one of the conductors 17 to 19 with the aid of this converter.
• this principle we will only observe the first pair of switches 11 and 12 to which the output conductor 17 is connected. Because the mode of operation of the other pairs of switches is practically the same except for a corresponding phase shift.
• Periods are plotted on the horizontal axis in FIG. 2.
• the present converter works with a basic interval, which is denoted by T and which is, for example, 10 microseconds.
• the shortest possible duration of the basic interval T is given by the clock frequency of the computer 5.
• the values of the direct voltage + Uo and -Uo supplied by the rectifier bridge 6 are plotted on the vertical axis.
• the first switch 11 is connected to the positive terminal + Uo and the second switch 12 is connected to the negative terminal -Uo of the bridge 6. If the first switch 11 is conductive and the second switch 12 is closed, then a positive direct voltage appears on the output conductor 17, namely during a time period t1 which is given by the duration of the opening of the switch 11. Conversely, if the second switch 12 is conductive, then a negative voltage appears on the output conductor 17 during a period t2.
• the thus time-limited voltages can be regarded as pulses being indicated at 28 a positive pulse and a 29 ne ⁇ gativer pulse ⁇ .
• a pair of switches, for example the pair 11 and 12 thus generates a pair of pulses 28, 29 of opposite polarity.
• n denotes the number of repetitions of the pulse pairs 28, 29 with the duration of t1 and t2, which appeared during the energy transmission between the supply network and the consumer 4.
• the length or width t1, t2 of the pulses 28, 29, which are used in the conversion, is a whole multiple of the basic interval T. 2 shows that first the second switch 12 was closed by the computer 5 and that this switch 12 remained closed for a period of time t2, so that a negative pulse 29 was generated, the length of which was six basic intervals T.
• the mean value of the electrical energy supplied to it is decisive. Because the "negative" energy was supplied for a total time n times t2 which was longer than the total time n times tl for the supply of the "positive" energy, the mean value of the resulting signal 31 on the conductor 17 is from the consumer's point of view 4th negative. Since the ratio between t1 and t2 has not changed during the energy supply, the resulting signal 31 has a constant amplitude.
• the resulting signal from the inverter 2 is indicated in FIG. 2 by a dash-dotted, horizontal line in order to indicate that the output signal 31 is a negative DC voltage of constant magnitude.
• the mean value changes, i.e. the amplitude of the output signal 31.
• the time period t21 for the riegative signal is initially approximately 7T and the time period t11 for the positive signal is only 1T.
• the length of time t1 i.e. the width of the positive pulse 28 has been continuously increased in steps of T during the operation of the converter.
• the time period t12 is already 3T and the time period t22 is only 5T. Since the ratio between the widths of the pulses 28, 29 (width modulation thereof) was continuously changed, the mean value of the energy supplied to the consumer 4 also changed. As a result, the amplitude of the output signal 31 is changed. In this case, the mean increases.
• the length of a step S is given by the total length of the time periods t1 and t2 of those successive pulse pairs 28, 29 in which the ratio of their widths t1 and t2 remained unchanged.
• the change in the amplitude of the output signal 31 can be gradual, as is the case according to FIG. 3, or this change can take place relatively quickly.
• 4 shows as an example a case in which the ratio between the time periods t1 and t2 is changed relatively quickly and at the same time in such a way that a resulting signal 31 is produced with increasing and decreasing amplitude.
• the computer 5 With curves 32, the amplitude of which changes rapidly, the computer 5 would have to work very quickly. This is because, taking into account the data influencing its mode of operation, it would have to supply the respectively adapted control signals for the duration of the next pair of pulses 28, 29 to the switches 11 to 16 for the duration of a pair of pulses 28, 29. Because this places very high demands on the computing speed of the computer 5, the signals required to control the switches 11 to 16 are only calculated at time intervals A (FIG. 4) which are greater than the duration of a pair of pulses, ie greater than t1 + t2. Between the times of two calculations, the switches 11 to 16 are controlled on the basis of sequences Q1, Q2, Q3 etc., which are derived from patterns stored in the computer 5. During the respective calculation, the computer 5 selects from the stored patterns that which is to be used as the basis for the control of the switches 11 to 16 until the next calculation.
• the time interval A between two calculations can even be longer than a plurality of stages S of the output signal 31 if the output signal 31 changes rapidly. 4, the * time interval A comprises three stages S. The calculation and selection of the stored patterns is therefore always carried out in advance for the next time period A.
• the patterns are stored in the memory of the computer 5, for example in the form of tables.
• a large number of such pulse patterns or tables are stored in the memory of the computer 5.
• that of the stored patterns is selected by the computer 5 which enables. to reach a section of the output signal 31 during the next time interval A, which approximates the desired curve 32 in this area to the maximum.
• a control sequence is derived from the selected pattern by the computer 5, which is used to control the switches 11 to 16. At the end of the respective control sequence, taking into account the current state of the converter, a further calculation is carried out and then, if necessary, a different pattern is selected, etc.
• the frequency of the control signal 30 is chosen higher than the frequency of the output signal 31 or 32 so that the output signal can be approximated at all.
• the switches 11 to 16 are switched over in a fixed time pattern, for example 20 microseconds. The resulting quantization of the amplitude is continuously recorded and also taken into account in later control sequences.
• the present converter is also designed to be in Depending on his load, his behavior can change.
• a signal supplied to the computer 5 by the monitoring unit 26 orients it, for example, via the current output current of the converter and thus the load on the consumer 4. If an increased load occurs, patterns for control sequences Q1, Q2, Q3 etc. are taken from the computer memory , which lower the frequency of the output signal 31 and thus also the speed of the motor 4. If the load 4 is excessive, the supply to the consumer 4 is interrupted.
• the program of the computer can be designed in such a way that the overcurrent signal is evaluated as a percentage. That is, it is determined whether the overcurrent signal is present rarely, often or continuously. This embodiment of the converter relates to FIG. 5.
• the switch-off time is changed, as can be seen from FIG. 5.
• the optical display 27 will shine stronger or weaker in the event of various overloads and the frequency is reduced until the overload conditions are eliminated again. If an overload condition persists for a longer period of time, an overload cut-off is carried out after a certain time, which is based on the percentage occurrence of the overload signal.
• the shutdown can be set in different stages. The same methods are also used to evaluate an overvoltage or undervoltage in the intermediate circuit and at overtemperature electronic components applied.
• the instantaneous value of the intermediate circuit current measured in the monitoring unit 26 can in particular also be used to calculate the load acting on the motor shaft.
• the respective measured value is recorded and evaluated at the moment the motor voltages 17 to 19 pass through zero.
• the magnetic field in the motor can be increased or decreased. In this way, for example, a voltage reduction and thus an energy saving can be achieved when the engine is under low load. This also effectively combats an electromechanical oscillation of the motor.
• the program of the computer 5 contains two sections.
• the first section of the program is used to calculate the frequency and amplitude of the output signal 32, taking into account specifications and circumstances determined during the operation of the converter.
• the computer receives a setpoint signal for the frequency of the output signal 32 via an analog-digital converter. This frequency is changed according to the setpoint depending on the selected settings for the ramp-up time and ramp-down time. A special hysteresis in the frequency tracking prevents oscillation between the individual acceptable frequencies.
• the frequency calculation is interrupted when the control signals forward and reverse are both switched off.
• the converter can be adapted to frequently occurring applications, such as double frequency of the motor signals etc.
• the amplitude Um of the output signal 32 is usually calculated according to a linear law Um «a.f + U1, where f is the frequency, a and U1 are constants. Both a and U1 can be set on the converter. In the area of lower frequencies, linear law is used depending on the choice of options.
• the second part of the computer program manages the patterns on which the control sequences are based.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Ac Motors In General (AREA)
• Inverter Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=4229128

Family Applications (1)

Country Status (3)

Families Citing this family (1)

Family Cites Families (2)

• 1986
  • 1986-06-03 CH CH224086A patent/CH669873A5/de not_active IP Right Cessation
• 1987
  • 1987-05-29 EP EP19870903232 patent/EP0268618A1/de not_active Withdrawn
  • 1987-05-29 WO PCT/CH1987/000060 patent/WO1987007789A1/de not_active Ceased

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events