Device for speed control of an asynchronous motor

A device for digital speed control of an asynchronous motor fed via a static converter, wherein

• (a) a pulse sequence f.sub.n, setting the set-point rotation speed, and a pulse sequence delivered by a rotation-speed measurement device coupled with the motor, which is proportional in its frequency to the actual rotation speed, is fed to two inputs of a digital up/down counter, where at the output of the counter, in case of coinciding input-pulse sequence frequencies, a digital signal is provided, which deviates from the mean value of a counter by an amount depending on the load, while during frequency deviation, a digital rotation-speed error signal occurs deviating upwardly or downwardly from this counter value;
• (b) a digital to analog converter follows the counter output, where the output signal of the digital to analog converter delivers the digital control signal for the converter after comparison with a voltage proportional to a set-point rotation speed via a voltage/frequency converter, the improvement comprising
• (c) an output (9) of the digital to analog converter (8) is placed in connection with a first input (11) of a summator (12), said summator (12) including a signal coincidence determining means;
• (d) a voltage depending on the rotation-speed set-point value (f.sub.n) and on the period duration (1/f.sub.i) of the rotation-speed measurement-device output signal (f.sub.i) is fed to a second input (23) of the summator (12);
• (e) an output (24) of the summator (12) is connected to a second input (25) of a multiplier (15);
• (f) the pulse sequence (f.sub.n), corresponding to the set-point rotation speed, is fed to an input (53) of a frequency/voltage converter (13);
• (g) the output (54) of the frequency/voltage converter (13) is connected to the other input (14) of the multiplier (15) and the output (54) feeds a voltage, proportional to the set-point rotation speed (f.sub.n), to the multiplier (15);
• (h) the output (26) of the multiplier (15) is connected with the voltage/frequency converter (27) and thereby to the motor.

A method for digital speed control of an asynchronous motor fed via a static converter comprising

• measuring rotation speed of a motor with a rotation speed measurement device having an output and coupled with the motor;
• delivering a first pulse sequence from the rotation speed measurement device, which first pulse sequence is proportional in its frequency to the actual rotation speed of the motor;
• feeding the first pulse sequence delivered by the rotation speed measurement device to a first input of a digital up/down counter, where the digital up/down counter has a first input connected to the output of the rotation speed measurement device, has a second input, and has an output;
• feeding a second pulse sequence f.sub.n for setting the set-point rotation speed to the second input of the digital up/down counter;
• supplying a digital signal at the output of the up/down counter in case of coinciding first input-pulse sequence and second input-pulse frequencies, which digital signal at the output of the up/down counter deviates from the mean value of a counter by an amount depending on the load, while during frequency deviation, a digital rotation-speed error signal occurs deviating upwardly or downwardly from this value of the up/down counter;
• passing an output signal from the up/down counter to a digital to analog converter having an input connected to the output of the up/down counter and having an output, where the digital to analog converter follows the up/down counter output;
• feeding a voltage depending on the rotation-speed set-point value (f.sub.n) and on the period duration (1/f.sub.i) of the rotation-speed measurement-device output signal (f.sub.i) to a second output of a summator wherein the summator has a first input and a second input and an output, where the output of the digital to analog converter is placed in connection with the first input of the summator;
• feeding a pulse sequence (f.sub.n), corresponding to a set-point rotation speed, to a first input of a frequency/voltage converter where the frequency voltage converter has a first input, a second input and an output, and where the output of the frequency/voltage converter is connected to the other input of a multiplier, said multiplier having a first input and an output, where an output of the summator is connected to the first input of a multiplier;
• feeding a voltage, proportional to the set-point rotation speed (f.sub.n), from the output of the frequency/voltage converter to the multiplier;
• comparing an output signal of the digital to analog converter with a voltage proportional to a set-point rotation speed via the voltage/frequency converter for obtaining a static power converter control signal, where the voltage/frequency converter has an input and an output, where the output of the multiplier is connected to the input of the voltage/frequency converter and where the output of the voltage/frequency converter is connected to the input of a static power converter;
• delivering the static power converter control signal to the static power converter having an input and an output;
• supplying an output power from the static power converter to the motor connected to the output of the static power converter.

A device for digital speed control of an asynchronous motor fed via a static power converter comprising

• (a) a static power converter having an input and an output;
• (b) a motor connected to said output
• (c) a rotational speed measurement device coupled with said motor and having an output delivering a first pulse sequence, which in its frequency f.sub.i is proportional to the actual speed of said motor;
• (d) a digital up/down counter means (4) having a first input (5) connected to the output of the speed measuring device for receiving said first pulse sequence, said counting means further having a second input and having an output, whereat a second pulse sequence having a frequency f.sub.n corresponding to a set-point rotational speed for said motor is fed to said second input of said counter means, and where said counter means provides at its output a digital signal, which in the case of said first and second pulse sequences having identical frequence corresponds to the mean count value of the counter means, and which digital output signal in case of a frequency deviation between said first and second pulse sequences is a digital speed error signal deviating upwardly or downwardly, respectively, from said mean count value of said counter means;
• (e) digital-to-analog converting means (8) having an input connected to the output of said counting means and having an output;
• (f) frequency-to-voltage converting means (13) receiving at its input said second pulse sequence;
• (g) time period-to-voltage converting means (17) having a first input (16), a second input (18) and an output (19), whereat its first input is connected to the output of said frequency-to-voltage converting means (13) and whereat its second input receives said first pulse sequence so that its output delivers a voltage depending on both the frequency f.sub.n of said second pulse sequence and the period duration 1/f.sub.i of said first pulse sequence;
• (h) summing means (12) having a first input (11), a second input (23) and an output (24), whereat said first input is placed in connection with the output of said D/A converting means (8), and said second input is placed in connection with the output of the time period-to-voltage converting means (12);
• (i) multiplying means (15) having first and second inputs and an output, whereat the first input (25) is connected to the output of said means and the second input (14) is connected to the output of said frequency-to-voltage converting means;
• (j) voltage-to-frequency converting (27) means having an input connected to the output of said multiplying means (15) and having an output connected to a frequency control input of said static power converter.

A device for digital speed control of an asynchronous motor via a static power converter, wherein

• (a) a first pulse sequence corresponding in its frequency f.sub.n to the set-point rotational speed of said motor and a second pulse sequence delivered by a speed measuring device coupled with said motor and corresponding in its frequency f.sub.i to the actual speed of the motor are fed to two inputs of a digital up/down counting means (4), whereat the output of said counting means in case of the frequencies of both pulse sequences being identical provides a digital output signal corresponding to the mean count value of said counting means, and which in the case of frequency deviation between the two pulse sequences provides a digital speed error signal deviating upwardly or downwardly, respectively from said mean count value;
• (b) a digital to analog converting means (8) is connected to the output of said counting means and the output signal of said converting means is compared with a voltage proportinal to a set-point speed of said motor, and a voltage-to-frequency converting means (27) supplied with a voltage resulting from said comparison delivers at its output a digital control signal for said static power converter;
• (c) an output of said digital-to-analog converting means (8) is placed in connection with a first input (11) of summing means (12);
• (d) first frequency-to-voltage converting means (13) is supplied with said first pulse sequence and delivers at its output a voltage corresponding to the set-point of the motor speed;
• (e) second frequency-to-voltage converting means (17) having a first input (16) connected to the output of said first frequency-to-voltage converting means and having a second input (18) receiving said second pulse sequence delivers a voltage depending on both the motor speed set point f.sub.n and the period duration 1/f.sub.i of the second pulse sequence f.sub.i which voltage is fed to a second input (23) of said summing means;
• (f) multiplying means (15) having two inputs and an output (26) is connected with its first input (25) to the output of said summing means and is connected with its second input (14) to the output of said first frequency-to-voltage converting means (13), whereat the output of said multiplying means is connected to the input of said voltage-to-frequency converting means (27).