Apparatus and method for measuring power factor and torque on the output of variable frequency drives

• US 5,003,252 A
• Filed: 08/16/1989
• Issued: 03/26/1991
• Est. Priority Date: 08/16/1989
• Status: Expired due to Term

• Current Assignee: Load Controls Incorporated
• Original Assignee: Load Controls Incorporated
• Inventors: Nystrom, Robert W.
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/394,562
• Time in Patent Office: 587 Days
• Field of Search: 324/158 MG, 324/83 R, 324/83 A, 324/83 D, 324/862.33, 324/862.34, 324/862.08, 318/490, 318/798, 318/805, 322/99
• US Class Current: 324/765.01
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines

Abstract

An apparatus and method for sensing power factor and torque on the output of a variable frequency machine is disclosed. Initially, power is sensed in each phase of the three-phase machine by utilizing Hall generators for multiplying the phase current flowing through each phase by a current proportional to a phase voltage for each phase. The products are then summed to obtain a reading of the instantaneous power drawn by the three phase machine. The AC component is filtered out of the summed signal using a multistage filter which allows for maintaining a fast response time with low ripple. This output is divided by the speed of the machine and multiplied by a constant to result in a signal representing torque. For measuring power factor, power signal sensed in each phase is applied to a DC blocking capacitor, effectively separating the AC envelope proportional to voltage times current. The three signals are applied to absolute value amplifiers and summed to provide a signal yielding total power. The instantaneous power is then divided by this signal to provide power factor.

Claims

1. A torque sensor for determining torque through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in a three-phase AC machine with speed to produce a resulting signal, said resulting signal representing sensed torque as an analog function, said torque sensor producing said signal within milliseconds, said sensor comprising:

means for measuring power in each phase of said three-phase AC machine, said means for measuring power being capable of measuring distorted and non-distorted sinusoidal and non-sinusoidal wave shapes while maintaining sensitivity at high and low frequencies, said means for measuring power including;

means for detecting a phase current from said phase of said three-phase AC machine to obtain a phase current signal;

means for detecting a phase voltage from said phase of said three-phase AC machine to obtain a phase voltage signal;

means for amplifying said phase voltage signal, said means for amplifying said phase voltage signal also acting to convert said phase voltage signal into a control current proportional to the phase voltage signal in amplitude and phase, said control current being temperature compensatable by means of a temperature compensating resistor; and

a Hall generator driven by said control current, said Hall generator configured and adapted to sense a magnetic field generated by the phase current signal, said Hall generator providing an output signal indicative of instantaneous power drawn by said phase of said three-phase AC machine;

said three-phase AC machine providing a summed output signal, said summed output signal being composed of a DC component and an AC component;

means for filtering said AC component from said summed output signal of said three-phase AC machine providing a filtered linear DC output signal, said means for filtering including at least four consecutive stages of filters, each of said stages of filters including an RC filter, said means for filtering capable of maintaining a ripple of about 1%;

means for measuring speed of the AC machine;

means for dividing the filtered linear DC output signal by the measured speed to provide an output proportional to torque of the machine.

2. The torque sensor according to claim 1 with means for compensating the measured speed such that the compensated measured speed is not permitted to equal zero.

3. The torque sensor according to claim 1 wherein the means for measuring speed of the AC machine produces a frequency proportional signal from the variable speed drive.

4. A power-factor sensor for sensing power-factor through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in a three-phase AC machine to produce a resulting signal, said resulting signal representing power-factor, said power-factor sensor producing said signal within milliseconds, said sensor comprising:

means for measuring power in each phase of said three-phase AC machine, said means for measuring power being capable of measuring distorted and non-distorted sinusoidal and non-sinusoidal wave shapes while maintaining sensitivity at high and lower frequencies, said means for measuring power including;

means for detecting a phase current from said phase of said three-phase AC machine to obtain a phase current signal;

means for detecting a phase voltage from said phase of said three-phase AC machine to obtain a phase voltage signal;

means for amplifying said phase voltage signal, said means for amplifying said phase voltage signal also acting to convert said phase voltage signal into a control current proportional to the phase voltage signal into a control current proportional to that phase voltage signal in amplitude and phase, said control current being temperature compensatable by means of a temperature compensating resistor; and

a Hall generator driven by said control current, said Hall generator configured and adapted to sense a magnetic field generated by the phase current signal, said Hall generator providing an output signal indicative of instantaneous power drawn by said phase of said three-phase AC machine;

said three-phase AC machine providing a summed output signal, said summed output signal being composed of a DC component and an AC component;

means for filtering said AC component from said summed output signal of said three-phase AC machine providing a filtered linear DC output signal, said means for filtering including at least four consecutive stages of filters, each of said stages of filters including an RC filter, said means for filtering capable of maintaining a ripple of about 1%;

means for blocking the DC component of each phase voltage signal and applying each output to an absolute value amplifier to produce a signal proportional to voltage multiplied by current;

means for summing each signal proportional to voltage multiplied by current to produce a total power signal;

means for filtering said total power signal, said means for filtering including at least four consecutive stages of filters each of said stages including an RC filter, said means for filtering capable of maintaining a ripple of approximately 1%; and

means for dividing the signal by the filtered linear DC output signal to produce a signal representing average power-factor.

5. A power factor sensor for sensing power-factor through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in a three-phase AC machine to produce a resulting signal, said resulting signal representing sensed power-factor as an analog function, said power-factor sensor producing said signal within milliseconds, said sensor comprising:

means for measuring power in each phase of said three-phase AC machine, said means for measuring power being capable of measuring distorted and non-distorted sinusoidal and non-sinusoidal wave shapes while maintaining sensitivity at high and low frequencies, said means for measuring power including;

means for detecting a phase current from said phase of said three-phase AC machine to obtain a phase current signal;

means for detecting a phase voltage from said phase of said three-phase AC machine to obtain a phase voltage signal;

means for amplifying said phase voltage signal, said means for amplifying said phase voltage signal also acting to convert said phase voltage signal into a control current proportional to the phase voltage signal in amplitude and phase, said control current being temperature compensatable by means of a temperature compensating resistor; and

a Hall generator driven by said control current, said Hall generator configured and adapted to sense a magnetic field generated by the phase current signal;

said Hall generator providing an output signal indicative of instantaneous power drawn by said phase of said three-phase AC machine;

means for blocking the DC component of each phase voltage signal and applying each output to an absolute value amplifier to produce a signal proportional to voltage multiplied by current;

means for summing each signal proportional to voltage multiplied by current to produce a total power signal proportional to VI;

said three-phase AC machine providing a summed output signal, said summed output signal being composed of a DC component and an AC component; and

means for dividing the absolute power signal by the summed output signal to provide a signal representing instantaneous power factor.

6. A sensor for power-dependent parameters, said sensor comprising:

means for measuring power in each phase of a three-phase AC machine having speed, said means for measuring power being capable of measuring distorted and non-distorted sinusoidal and non-sinusoidal wave shapes while maintaining sensitivity at high and lower frequencies, said means for measuring power including;

means for detecting a phase current from a phase of said three-phase AC machine to obtain a phase current signal;

means for detecting a phase voltage from a phase of said three-phase AC machine to obtain a phase voltage signal;

means for amplifying said phase voltage signal, said means for amplifying the phase voltage signal also acting to convert the phase voltage signal into a control current proportional to the phase voltage signal in amplitude and phase, said control current being temperature compensatable by means of a temperature compensating resistor; and

a Hall generator driven by said control current, said Hall generator configured and adapted to sense a magnetic field generated by the phase current signal, said Hall generator providing an output signal indicative of instantaneous power drawn by said phase of said three-phase AC machine;

said three-phase AC machine providing a summed output signal, said summed output signal being composed of a DC component and an AC component; and

means for filtering said AC component from said summed output signal of said three-phase AC machine providing a filtered linear DC output signal, said means for filtering including at least four consecutive stages of filters, each of said stages of filters including an RC filter, said means for filtering capable of maintaining a ripple of about 1%.

7. The sensor of claim 6 where the power-dependent parameters are torque and power-factor.

8. A sensor in accordance with claim 6, wherein the power-dependent parameter is torque, said sensor sensing torque through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in the three-phase AC machine to produce a resulting signal, said resulting signal representing sensed torque as an analog function, said sensor producing the resulting signal within milliseconds, said sensor comprising:

means for measuring speed of the AC machine;

means for dividing the filtered linear DC output signal by the measured speed to produce an output signal being proportional to said sensed torque of the AC machine.

9. The torque sensor according to claim 8 with means for compensating the measured speed such that the compensated measured speed is not permitted to equal to zero.

10. The torque sensor according to claim 8 wherein the means for measuring speed of the AC machine produces a frequency proportional signal from the AC machine.

11. The torque sensor according to claim 10 wherein the AC machine is a variable frequency drive.

12. A sensor in accordance with claim 6, wherein the power-dependent parameter is power-factor, said sensor sensing power-factor through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in a three-phase AC machine to produce a resulting signal, said resulting signal representing sensed power-factor, said power-factor sensor producing said signal within milliseconds, said sensor comprising:

means for blocking the DC component of each phase voltage signal and applying each output to an absolute value amplifier to produce a signal proportional to voltage multiplied by current;

means for summing each signal proportional to voltage multiplied by current to produce a total power signal;

means for filtering said total power signal, said means for filtering including at least four consecutive stages of filters, each of said stages including an RC filter, said means for filtering capable of maintaining a ripple of approximately 1%; and

means for dividing the signal by the filtered linear DC output signal to produce an output signal being representative of sensed average power-factor of the AC machine.

13. A sensor in accordance with claim 6, wherein the power-dependent parameter is power-factor, said sensor sensing power-factor through a wide bandwidth of frequencies, continuously and automatically, at any moment in time in a three-phase AC machine to produce a resulting signal, said resulting signal representing sensed power-factor being a continuous analog function, said power factor sensor producing said signal within milliseconds, said sensor comprising:

means for blocking the DC component of each phase voltage signal and applying each output to an absolute value amplifier to produce a signal proportional to voltage multiplied by current;

means for summing each signal proportional to voltage multiplied by current to produce a total power signal;

means for dividing the absolute power signal by the summed output signal to produce an output signal being representative of sensed instantaneous power-factor of the AC machine.