CN105676125B - Variable-frequency motor power measurement method and device - Google Patents
Variable-frequency motor power measurement method and device Download PDFInfo
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- CN105676125B CN105676125B CN201610029405.7A CN201610029405A CN105676125B CN 105676125 B CN105676125 B CN 105676125B CN 201610029405 A CN201610029405 A CN 201610029405A CN 105676125 B CN105676125 B CN 105676125B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/34—Testing dynamo-electric machines
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- G—PHYSICS
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- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
- G01L3/24—Devices for determining the value of power, e.g. by measuring and simultaneously multiplying the values of torque and revolutions per unit of time, by multiplying the values of tractive or propulsive force and velocity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R21/06—Arrangements for measuring electric power or power factor by measuring current and voltage
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Abstract
The present invention relates to a kind of variable-frequency motor power measurement method, this method includes：The real and imaginary parts of fundamental wave vector of corresponding each phase voltage and the real part of harmonic vector and imaginary part are determined according to each the first input voltage of phase；The real and imaginary parts of fundamental wave vector of corresponding each phase current and the real part of harmonic vector and imaginary part are determined according to each the first input current of phase；Corresponding the first active power of each phase and the first reactive power are determined with imaginary part with the real and imaginary parts of fundamental wave vector and the real part of harmonic vector of imaginary part and each phase current according to the real and imaginary parts of fundamental wave vector of each phase voltage, the real part of harmonic vector；Total active power of variable-frequency motor and total reactive power are determined according to each the first active power of phase and the first reactive power.This method can realize the measurement to the real-time online power of variable-frequency motor.In addition, also correspondence provides a kind of variable-frequency motor power-measuring device.
Description
Technical Field
The invention relates to the field of electronic equipment, in particular to a method and a device for measuring power of a variable frequency motor.
Background
The modern manufacturing industry requires a great deal of machine tool equipment, one of the core components of which is the motor. Compared with a fixed-frequency motor, the variable-frequency motor used in the machine tool equipment can achieve better energy-saving and emission-reduction effects and can realize stepless speed regulation of a machine tool spindle. The real-time power of the variable frequency motor can reflect the current working state of the machine tool, and if the stress conditions of the cutter and the workpiece of the machine tool in the operation process can be known according to the real-time online power of the variable frequency motor, the problems existing in the machining process can be timely and efficiently found and solved. Therefore, the real-time online power of the variable frequency motor is obtained with great significance.
Conventional power measurement methods for motors, such as those using spectral analysis or quasi-synchronous measurement, are measurements of power performed by the motor to determine the frequency of a point. The traditional measurement method cannot achieve real-time online power acquisition of the variable frequency motor.
Disclosure of Invention
In view of the above, it is necessary to provide a method and an apparatus for measuring power of an inverter motor, which can realize real-time online measurement of power of the inverter motor.
A method of variable frequency motor power measurement, the method comprising: acquiring a first input voltage and a first input current of each phase of a variable frequency motor under the working condition; determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each phase voltage according to the first input voltage of each phase; determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each corresponding phase current according to the first input current of each phase; determining corresponding first active power and first passive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector; and determining the total active power and the total reactive power of the variable frequency motor according to the first active power and the first reactive power of each phase.
In one embodiment, the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each phase voltage according to the first input voltage of each phase comprises: for a first input voltage of each phase, converting the first input voltage into an input voltage in the form of a Fourier series; determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series; the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the first input current of each phase comprises the following steps: for a first input current of each phase, converting the first input current into an input current in the form of a Fourier series; and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
A method of variable frequency motor power measurement, the method comprising: acquiring second input voltage and second input current of each phase of the variable frequency motor after a voltage transformer and a current transformer are added; determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each phase voltage according to the second input voltage of each phase; determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each corresponding phase current according to the second input current of each phase; determining corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector; acquiring a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after a voltage transformer and a current transformer are added; determining a third active power and a third reactive power of a corresponding phase of actual input of the variable frequency motor according to the second active power, the second reactive power and the phase difference change value; and determining the total active power and the total reactive power of the variable frequency motor according to the third active power and the third reactive power of each phase.
In one embodiment, the step of obtaining a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after adding a voltage transformer and a current transformer includes: acquiring each phase of third input voltage and third input current of the variable frequency motor under a rated working condition; determining a third phase difference of a corresponding phase according to the third input voltage and the third input current of each phase; and determining a corresponding phase difference change value according to the third phase difference.
In one embodiment, the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each phase voltage according to the second input voltage of each phase comprises: for a second input voltage of each phase, converting the second input voltage into an input voltage in the form of a Fourier series; determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series; the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to each phase of second input current comprises the following steps: for a second input current of each phase, converting the second input current into an input current in the form of a Fourier series; and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
An inverter motor power measurement apparatus, the apparatus comprising: the first input voltage acquisition module is used for acquiring the first input voltage of each phase of the variable frequency motor under the working condition; the first input current acquisition module is used for acquiring the first input current of each phase of the variable frequency motor under the working condition; the first input voltage determining module is used for determining the real part and the imaginary part of a fundamental wave vector and the real part and the imaginary part of a harmonic wave vector of each corresponding phase voltage according to the first input voltage of each phase; the first input current determining module is used for determining the real part and the imaginary part of a fundamental wave vector and the real part and the imaginary part of a harmonic wave vector of each corresponding phase current according to the first input current of each phase; a first phase power determination module, configured to determine corresponding first active power and first reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current, and the real part and the imaginary part of the harmonic wave vector; and the first power determination module is used for determining the total active power and the total reactive power of the variable frequency motor according to the first active power and the first reactive power of each phase.
In one embodiment, the first input voltage determination module is further configured to convert the first input voltage into an input voltage in the form of a fourier series for each phase of the first input voltage; determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series; the first input current determination module is further used for converting the first input current into an input current in a Fourier series form for the first input current of each phase; and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
An inverter motor power measurement apparatus, the apparatus comprising: the second input voltage acquisition module is used for acquiring second input voltage of each phase of the variable frequency motor after the voltage transformer and the current transformer are added; the second input current acquisition module is used for acquiring second input current of each phase of the variable frequency motor after the voltage transformer and the current transformer are added; the second input voltage determining module is used for determining the real part and the imaginary part of a fundamental wave vector and the real part and the imaginary part of a harmonic wave vector of each corresponding phase voltage according to the second input voltage of each phase; the second input current determining module is used for determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the second input current of each phase; the second phase power determination module is used for determining corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector; the phase difference change value determining module is used for acquiring a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after a voltage transformer and a current transformer are added; the third phase power determining module is used for determining third active power and third reactive power of the corresponding phase of the actual input of the variable frequency motor according to the second active power, the second reactive power and the phase difference change value; and the third power determination module is used for determining the total active power and the total reactive power of the variable frequency motor according to the third active power and the third reactive power of each phase.
In one embodiment, the phase difference change value determining module is further configured to obtain a third input voltage and a third input current of each phase of the variable frequency motor under a rated working condition; determining a third phase difference of a corresponding phase according to the third input voltage and the third input current of each phase; and determining a corresponding phase difference change value according to the third phase difference.
In one embodiment, the second input voltage determination module is further configured to, for a second input voltage of each phase, convert the second input voltage into an input voltage in the form of a fourier series; determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series; the second input current determination module is further used for converting the second input current into an input current in a Fourier series form for the second input current of each phase; and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
The method and the device for measuring the power of the variable frequency motor can realize real-time on-line power measurement of the variable frequency motor. And the working characteristics of the variable frequency motor can be monitored in time, and the working condition of the variable frequency motor is analyzed, so that the motor can be effectively controlled subsequently. Meanwhile, the stress conditions of the cutter and the workpiece of the equipment comprising the variable frequency motor in the machining process can be analyzed according to the measured real-time online power of the variable frequency motor, the working state of the equipment can be mastered in real time, and the problems existing in the machining process can be timely and efficiently found and solved.
Drawings
FIG. 1 is a schematic flow chart of a method for measuring power of a variable frequency motor according to an embodiment;
FIG. 2 is a schematic flow chart of the steps for determining the real and imaginary components of the fundamental vector and the real and imaginary components of the harmonic vector for each phase voltage based on the first input voltage for each phase in one embodiment;
FIG. 3 is a flowchart illustrating the steps for determining the real and imaginary components of the fundamental vector and the real and imaginary components of the harmonic vector for each phase current based on the first input current for each phase in one embodiment;
FIG. 4 is a schematic flow chart of a method for measuring power of a variable frequency motor according to another embodiment;
FIG. 5 is a schematic flow chart of a method for measuring power of a variable frequency motor in yet another embodiment;
FIG. 6 is a schematic flowchart illustrating steps of obtaining a corresponding phase difference change value between an input voltage and an input current of each phase of the inverter motor after a voltage transformer and a current transformer are added in one embodiment;
FIG. 7 is a schematic flow chart of a method for measuring power of a variable frequency motor according to one embodiment;
FIG. 8 is a flow chart illustrating a method for measuring power of a variable frequency motor according to another embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In one embodiment, as shown in FIG. 1, a method for measuring power of a variable frequency motor is provided, and the method comprises the following steps 102-110.
And 102, acquiring a first input voltage and a first input current of each phase of the variable frequency motor under the working condition.
In this embodiment, the inverter motor includes a three-phase inverter motor, and may be an inverter motor applied to machine tool equipment in modern manufacturing industry. For example, the motor can be an inverter motor applied to equipment such as a compressor, a water pump, a crusher, a cutting machine tool, a transport machine and the like.
Specifically, the first input voltage is an instantaneous input voltage of the variable frequency motor in a working state; the first input current is the instantaneous input current of the variable frequency motor in the working state. The instantaneous input voltage and instantaneous input current are typically varied cyclically in a sinusoidal fashion as a function of time.
The terminal may specifically use instantaneous input voltage data and instantaneous input current data of each phase of the inverter motor, which are measured by a voltage measuring device, a current measuring device, and the like, as the first input voltage and the first input current of the corresponding phase, that is, the a-phase first input voltage and the a-phase first input current, the B-phase first input voltage and the B-phase first input current, and the C-phase first input voltage and the C-phase first input current.
And 104, determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase voltage according to the first input voltage of each phase.
And 106, determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the first input current of each phase.
In this embodiment, the first input voltage and the first input current are generally in the form of a sinusoidal voltage signal and a sinusoidal current signal. Therefore, the first input voltage and the first input current can be respectively subjected to certain mathematical transformation and converted into a specific expression form, the fundamental wave vector and the harmonic wave vector of each phase voltage and current can be correspondingly obtained, and the real part and the imaginary part of the fundamental wave vector, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase voltage and the real part and the imaginary part of the harmonic wave vector can be further obtained.
In one embodiment, as shown in fig. 2, the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each phase voltage according to the first input voltage of each phase includes:
step 202, for the first input voltage of each phase, converting the first input voltage into an input voltage in the form of a fourier series.
Specifically, the a-phase first input voltage of the inverter motor obtained at time t is denoted as f1(t) the f can be transformed according to the Fourier transform method1(t) is changed to
Wherein,is a DC component of the A-phase first input voltage signal, a1kAnd b1kThe amplitude of the real part and the amplitude of the imaginary part of the k-th harmonic of the A-phase first input voltage signal are respectively, and k omega is the angular frequency of the variable frequency motor under the current working condition. When k is 1, i.e. when a1kAnd b1kAre respectively a11And b11The amplitudes of the real and imaginary parts of the fundamental wave of the a-phase first input voltage signal are indicated, respectively.
In step 204, the real part and imaginary part of the fundamental wave vector and the real part and imaginary part of the harmonic wave vector of the corresponding phase voltage are determined by performing discrete fourier transform on the input voltage in the form of fourier series.
Specifically, f can be adjusted to1(t) AD sampling, DFT (Discrete Fourier Transform) conversion, transforming it into:
then
Wherein f is1(k) Is f1And (t) the amplitude of the kth sampling, u is a weighting coefficient of the phase, and can be a corresponding preset numerical value, and N is the number of sampling points of the signal in one period.
Similarly, the same transformation and processing are performed on the first input voltages of other phases, so that the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of the first input voltage of the corresponding phase can be obtained respectively.
In one embodiment, as shown in fig. 3, the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the first input current of each phase includes:
step 302, for the first input current of each phase, converting the first input current into an input current in the form of a fourier series.
Specifically, similar to the processing method of the first input voltage, the a-phase first input current of the inverter motor obtained at the time t is denoted as f2(t) the f can be transformed according to the Fourier transform method2(t) is changed to
Wherein,is a direct current component of the A-phase first input current signal, a2kAnd b2kThe amplitude of the real part and the amplitude of the imaginary part of the k-th harmonic of the A-phase first input current signal are respectively, and k omega is the angular frequency of the variable frequency motor under the current working condition. When k is 1, i.e. when a2kAnd b2kAre respectively a21And b21The amplitudes of the real part and the imaginary part of the fundamental wave of the a-phase first input current signal are respectively represented.
In step 304, the real and imaginary parts of the corresponding phase current fundamental wave vector and the real and imaginary parts of the harmonic wave vector are determined by discrete fourier transform of the input current in the form of a fourier series.
Specifically, f can be adjusted to2(t) AD sampling and performingDFT (Discrete Fourier Transform) Transform, transforming it into:
then
Wherein f is2(k) Is f2And (t) the amplitude of the kth sampling, u is a weighting coefficient of the phase, and can be a corresponding preset numerical value, and N is the number of sampling points of the signal in one period.
Similarly, the same transformation and processing are performed on the first input voltages of other phases, so that the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of the first input voltage of the corresponding phase can be obtained respectively.
And step 108, determining the corresponding first active power and the corresponding first reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector.
Specifically, the fundamental wave amplitude of the first active power and the fundamental wave amplitude of the first inactive power of the corresponding phase may be determined according to the real part and the imaginary part of the fundamental wave vector of each phase voltage and the real part and the imaginary part of the fundamental wave vector of the current of the corresponding phase; and determining the k-th harmonic amplitude of the first active power and the k-th harmonic amplitude of the first inactive power of the corresponding phase according to the real part and the imaginary part of the k-th harmonic vector of each phase voltage and the real part and the imaginary part of the k-th harmonic vector of the current of the corresponding phase.
Determining the amplitude of the first active power of the corresponding phase according to the fundamental wave amplitude and the k-th harmonic amplitude of the first active power of each phase; and determining the amplitude of the first reactive power of the corresponding phase according to the fundamental wave amplitude and the k-th harmonic amplitude of the first reactive power of each phase.
Specifically, the amplitude of the first active power is the sum of the corresponding first active power fundamental amplitude and all the k-order harmonic amplitudes; the amplitude of the first reactive power is the sum of the corresponding first reactive power fundamental amplitude and all the k-th harmonic amplitudes.
Specifically, the relationship therebetween can be expressed as:
wherein, PkIs the amplitude of the k-th harmonic of the first active power, when k is 1, then P is the amplitude of the first active powerkIs namely P1Representing the magnitude of the fundamental wave of the first active power; qkThe amplitude of the first reactive power is k is 1, and Q is the valuekIs namely Q1Representing the magnitude of the fundamental wave of the first active power; ptotalIs the amplitude of the first active power; qtotalIs the magnitude of the first reactive power. u. ofak、ubkRespectively representing the real part and the imaginary part of a k-th harmonic vector of the first input voltage; i.e. iak、ibkRepresenting the real and imaginary parts, respectively, of the K-th harmonic vector of the first input current.
It will be appreciated that although in theory the value of k is infinite, in practice as k increases, the corresponding value of the k harmonic component becomes smaller and smaller, and the guidance is negligible. Therefore, in practice, the upper limit value of k may be preset to a specific upper limit value. The amplitude of the first active power is the sum of the amplitudes of the corresponding fundamental wave and the harmonic wave when k is 1 to k is a preset upper limit value.
And step 110, determining total active power and total reactive power of the variable frequency motor according to the first active power and the first reactive power of each phase.
Specifically, as shown in fig. 4, after the first active power and the first reactive power of each phase are determined, the corresponding first active power and the corresponding first reactive power of each phase may be superimposed, so that the total active power and the total reactive power of the inverter motor may be obtained. The total active power and the total reactive power can reflect the real-time online power of the variable frequency motor.
According to the method for measuring the power of the variable frequency motor, the real-time online power measurement of the variable frequency motor can be realized through the steps. And the working characteristics of the variable frequency motor can be monitored in time, and the working condition of the variable frequency motor is analyzed, so that the motor can be effectively controlled subsequently. Meanwhile, the stress conditions of the cutter and the workpiece of the equipment comprising the variable frequency motor in the machining process can be analyzed according to the measured real-time online power of the variable frequency motor, the working state of the equipment can be mastered in real time, and the problems existing in the machining process can be timely and efficiently found and solved.
In one embodiment, as shown in FIG. 5, a further method for measuring power of a variable frequency motor is provided, the method comprises the following steps 502-514.
And 502, acquiring second input voltage and second input current of each phase of the variable frequency motor after a voltage transformer and a current transformer are added.
In this embodiment, the inverter motor includes a three-phase inverter motor, and may be an inverter motor applied to machine tool equipment in modern manufacturing industry. For example, the motor can be an inverter motor applied to equipment such as a compressor, a water pump, a crusher, a cutting machine tool, a transport machine and the like.
Specifically, the second input voltage is an instantaneous input voltage of the variable frequency motor in a working state; the second input current is the instantaneous input current of the variable frequency motor in the working state. The instantaneous input voltage and instantaneous input current are typically varied cyclically in a sinusoidal fashion as a function of time.
In this embodiment, a voltage transformer (PT) and a Current Transformer (CT) may be added to the inverter motor, and the voltage transformer and the Current transformer may be used to change or adjust the phases of the operating voltage and the operating Current of the inverter motor. Changes in the phase of the operating voltage and operating current result in changes in the corresponding active and reactive power, but the apparent power is not changed.
The terminal can specifically use instantaneous input voltage data and instantaneous input current data of each phase of the variable frequency motor, which are measured by the voltage measuring device, the current measuring device and the like and added with the voltage transformer and the current transformer, as second input voltage and second input current of a corresponding phase, namely, a-phase second input voltage and a-phase second input current, B-phase second input voltage and B-phase second input current, and C-phase second input voltage and C-phase second input current.
And step 504, determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase voltage according to the second input voltage of each phase.
And step 506, determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the second input current of each phase.
In this embodiment, the second input voltage and the second input current are generally in the form of a sinusoidal voltage signal and a sinusoidal current signal. Therefore, certain mathematical transformation can be respectively carried out on the second input voltage and the second input current, the second input voltage and the second input current are converted into a specific expression form, the fundamental wave vector and the harmonic wave vector of each phase voltage and current can be correspondingly obtained, and then the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector can be obtained.
In one embodiment, the step of determining the real and imaginary parts of the fundamental vector and the real and imaginary parts of the harmonic vector of each phase voltage corresponding to each phase second input voltage comprises: for the second input voltage of each phase, converting the second input voltage into an input voltage in the form of a Fourier series; the real and imaginary parts of the fundamental wave vector and the real and imaginary parts of the harmonic wave vector of the corresponding phase voltage are determined by discrete fourier transform of the input voltage in the form of a fourier series.
Specifically, the a-phase second input voltage of the inverter motor obtained at time t is denoted as f3(t) the f can be transformed according to the Fourier transform method3(t) is changed to
Wherein,is a DC component of the A-phase second input voltage signal, a3kAnd b3kThe amplitude of the real part and the amplitude of the imaginary part of the k-th harmonic of the A-phase second input voltage signal are respectively, and k omega is the angular frequency of the variable frequency motor under the current working condition. When k is 1, i.e. when a3kAnd b3kAre respectively a31And b31And respectively representing the amplitudes of the real part and the imaginary part of the fundamental wave of the A-phase second input voltage signal.
Further, f can be adjusted to3(t) AD sampling, DFT conversion, and transforming into:
then
Wherein f is3(k) Is f3And (t) the amplitude of the kth sampling, u is a weighting coefficient of the phase, and can be a corresponding preset numerical value, and N is the number of sampling points of the signal in one period.
Similarly, the same transformation and processing are performed on the second input voltages of other phases, so that the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of the second input voltage of the corresponding phase can be obtained respectively.
In one embodiment, the step of determining the real and imaginary parts of the fundamental vector and the real and imaginary parts of the harmonic vector of each phase voltage corresponding to each phase second input voltage comprises: for the second input current of each phase, converting the second input current into an input current in the form of a Fourier series; the real and imaginary parts of the corresponding phase current fundamental vector and the real and imaginary parts of the harmonic vector are determined by discrete fourier transforming the input current in the form of a fourier series.
Specifically, similar to the processing method of the second input voltage, the a-phase second input current of the inverter motor obtained at the time t is denoted as f4(t) the f can be transformed according to the Fourier transform method4(t) is changed to
Wherein,is a DC component of the A-phase second input current signal, a4kAnd b4kThe amplitude of the real part and the amplitude of the imaginary part of the k-th harmonic of the A-phase second input current signal are respectively, and k omega is the current working condition of the variable frequency motorMoreover the angular frequency. When k is 1, i.e. when a4kAnd b4kAre respectively a41And b41And respectively representing the amplitudes of the real part and the imaginary part of the fundamental wave of the A-phase second input current signal.
Further, f can be adjusted to4(t) AD sampling, DFT (Discrete Fourier Transform) conversion, transforming it into:
then
Wherein f is4(k) Is f4And (t) the amplitude of the kth sampling, u is a weighting coefficient of the phase, and can be a corresponding preset numerical value, and N is the number of sampling points of the signal in one period.
Similarly, the same transformation and processing are performed on the second input voltages of other phases, so that the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of the second input voltage of the corresponding phase can be obtained respectively.
And step 508, determining corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector.
Specifically, the fundamental wave amplitude of the second active power and the fundamental wave amplitude of the second reactive power of the corresponding phase may be determined according to the real part and the imaginary part of the fundamental wave vector of each phase voltage and the real part and the imaginary part of the fundamental wave vector of the current of the corresponding phase; and determining a second active power k harmonic amplitude and a second reactive power k harmonic amplitude of the corresponding phase according to the real part and the imaginary part of the k harmonic vector of each phase voltage and the real part and the imaginary part of the k harmonic vector of the current of the corresponding phase.
Determining the amplitude of the second active power of the corresponding phase according to the fundamental wave amplitude and the k-th harmonic amplitude of the second active power of each phase; and determining the amplitude of the second reactive power of the corresponding phase according to the fundamental wave amplitude and the k-th harmonic amplitude of the second reactive power of each phase.
Specifically, the amplitude of the second active power is the sum of the corresponding second active power fundamental amplitude and all the k-order harmonic amplitudes; the amplitude of the second reactive power is the sum of the corresponding second reactive power fundamental amplitude and all the k-th harmonic amplitudes.
Specifically, the relationship therebetween can be expressed as:
wherein, PkIs the amplitude of the k harmonic of the second active power, when k is 1, then P is the amplitude of the k harmonic of the second active powerkIs namely P1Representing the amplitude of the fundamental wave of the second active power; qkThe amplitude of the second reactive power, when k is 1, Q is thenkIs namely Q1Representing the amplitude of the fundamental wave of the second active power; ptotalIs the amplitude of the second active power; qtotalIs the magnitude of the second reactive power. u. ofak、ubkRepresenting the real and imaginary part of the k-th harmonic vector of the second input voltage, respectivelyA section; i.e. iak、ibkRepresenting the real and imaginary parts, respectively, of the K-th harmonic vector of the second input current.
It will be appreciated that although in theory the value of k is infinite, in practice as k increases, the corresponding value of the k harmonic component becomes smaller and smaller, and the guidance is negligible. Therefore, in practice, the upper limit value of k may be preset to a specific upper limit value. The amplitude of the second active power is the sum of the amplitudes of the corresponding fundamental wave and the harmonic wave when k is 1 to k is a preset upper limit value.
And step 510, acquiring a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after the voltage transformer and the current transformer are added.
In this embodiment, due to the existence of the CT and the PT, both the phases of the working input voltage and the input current of the inverter motor can be changed. Specifically, for the input current and the input voltage of the inverter motor of each phase, taking phase a as an example, it can be noted that after CT is added, the phase difference of the input current isAfter PT is added, the phase difference of the input voltage isThe phase difference between the sum of the input current and the input voltage after passing through PT and CT varies by the value
In one embodiment, as shown in fig. 6, the step of obtaining the corresponding phase difference change value between each phase of input voltage and input current of the inverter motor after adding the voltage transformer and the current transformer includes:
step 602, obtaining a third input voltage and a third input current of each phase of the variable frequency motor under a rated working condition.
Step 604, determining a third phase difference of the corresponding phase according to the third input voltage and the third input current of each phase.
Step 606, determining a corresponding phase difference change value according to the third phase difference.
In this embodiment, the third input voltage and the third input current are rated input values of the inverter motor, respectively. Under the rated working condition of the variable frequency motor, an included angle between a third input voltage and a third input current of the variable frequency motor is a fixed value, namely, a third phase difference is a fixed value. The system can acquire the fixed phase difference of the variable frequency motor, and further can calculate the phase difference change value between the input voltage and the input current of the variable frequency motor after the CT and the PT are added according to the phase difference.
And step 512, determining a third active power and a third reactive power of the corresponding phase of the actual input of the variable frequency motor according to the second active power, the second reactive power and the phase difference change value.
In this embodiment, for the second active power and the second reactive power of each phase, taking phase a as an example, the second active power may be P ', the second active power may be Q', effective values of the current and the voltage actually input to the inverter motor are I and V, the phase difference is Φ, and the corresponding third active power and third reactive power are P and Q.
Then according to the power triangle principle, there is the following relationship between them:
recording the correction factorAccording to the aboveThe relationship, one can get:
P＝k1P'+k2Q'，Q＝k1Q'-k2P'
and step 514, determining the total active power and the total reactive power of the variable frequency motor according to the third active power and the third reactive power of each phase.
After the third active power and the third reactive power of each phase are determined, the corresponding third active power and third reactive power of each phase can be superposed, and then the total active power and the total reactive power of the variable frequency motor can be obtained. The total active power and the total reactive power can reflect the real-time online power of the variable frequency motor.
According to the method for measuring the power of the variable frequency motor, after the CT and the PT are added, the corresponding phase difference change value between the input voltage and the input current of each phase, the corresponding second active power and the corresponding second reactive power are determined, and then the total active power and the total reactive power of the variable frequency motor can be determined according to the power triangle principle. By adopting the method, the measured total active power and the measured total reactive power of the variable frequency motor can be more accurate. And then can more accurately monitor inverter motor operating characteristics according to inverter motor's real-time online power to the condition of doing work of analysis inverter motor, so that follow-up effectively control the motor. Meanwhile, the stress conditions of the cutter and the workpiece of the equipment comprising the variable frequency motor in the machining process can be analyzed according to the real-time online power of the variable frequency motor, the working state of the equipment can be mastered in real time, and the problems existing in the machining process can be timely and efficiently found and solved.
In one embodiment, as shown in fig. 7, there is provided a variable frequency motor power measuring apparatus, the apparatus comprising:
the first input voltage obtaining module 702 is configured to obtain a first input voltage of each phase of the inverter motor under operation.
And a first input current obtaining module 704, configured to obtain a first input current of each phase of the variable frequency motor in operation.
And a first input voltage determining module 706 for determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each phase voltage according to the first input voltage of each phase.
A first input current determining module 708 for determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the first input current of each phase.
And a first phase power determination module 710 for determining the corresponding first active power and first reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current, and the real part and the imaginary part of the harmonic wave vector.
And a first power determining module 712, configured to determine a total active power and a total reactive power of the inverter motor according to the first active power and the first reactive power of each phase.
In one embodiment, the first input voltage determination module 706 is further configured to convert the first input voltage into an input voltage in the form of a fourier series for each phase of the first input voltage; the real and imaginary parts of the fundamental wave vector and the real and imaginary parts of the harmonic wave vector of the corresponding phase voltage are determined by discrete fourier transform of the input voltage in the form of a fourier series.
The first input current determination module 708 is further configured to convert the first input current into an input current in the form of a fourier series for the first input current of each phase; the real and imaginary parts of the corresponding phase current fundamental vector and the real and imaginary parts of the harmonic vector are determined by discrete fourier transforming the input current in the form of a fourier series.
In one embodiment, as shown in fig. 8, another variable frequency motor power measuring apparatus is provided, the apparatus comprising:
and a second input voltage obtaining module 802, configured to obtain a second input voltage of each phase of the variable frequency motor after a voltage transformer and a current transformer are added.
And a second input current obtaining module 804, configured to obtain a second input current of each phase of the variable frequency motor after the voltage transformer and the current transformer are added.
And a second input voltage determining module 806, configured to determine a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each phase voltage according to the second input voltage of each phase.
And a second input current determining module 808, configured to determine a real part and an imaginary part of the fundamental wave vector and a real part and an imaginary part of the harmonic wave vector of each corresponding phase current according to each phase second input current.
The second phase power determination module 810 determines corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current, and the real part and the imaginary part of the harmonic wave vector.
And a phase difference change value determining module 812, configured to obtain a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after the voltage transformer and the current transformer are added.
And a third phase power determining module 814, configured to determine, according to the second active power, the second reactive power, and the phase difference change value, a third active power and a third reactive power of a corresponding phase of the actual input of the inverter motor.
And a third power determining module 816, configured to determine a total active power and a total reactive power of the inverter motor according to the third active power and the third reactive power of each phase.
In one embodiment, the phase difference change value determining module 814 is further configured to obtain a third input voltage and a third input current of each phase of the inverter motor under a rated operating condition; determining a third phase difference of a corresponding phase according to the third input voltage and the third input current of each phase; and determining a corresponding phase difference change value according to the third phase difference.
In one embodiment, the second input voltage determining module 806 is further configured to convert the second input voltage into an input voltage in the form of a fourier series for the second input voltage of each phase; the real and imaginary parts of the fundamental wave vector and the real and imaginary parts of the harmonic wave vector of the corresponding phase voltage are determined by discrete fourier transform of the input voltage in the form of a fourier series.
The second input current determination module 808 is further configured to convert the second input current into an input current in the form of a fourier series for the second input current of each phase; the real and imaginary parts of the corresponding phase current fundamental vector and the real and imaginary parts of the harmonic vector are determined by discrete fourier transforming the input current in the form of a fourier series.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (6)
1. A method for measuring power of a variable frequency motor is characterized by comprising the following steps:
acquiring second input voltage and second input current of each phase of the variable frequency motor after a voltage transformer and a current transformer are added;
determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each phase voltage according to the second input voltage of each phase;
determining a real part and an imaginary part of a fundamental wave vector and a real part and an imaginary part of a harmonic wave vector of each corresponding phase current according to the second input current of each phase;
determining corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector;
acquiring a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after a voltage transformer and a current transformer are added;
determining a third active power and a third reactive power of a corresponding phase of actual input of the variable frequency motor according to the second active power, the second reactive power and the phase difference change value;
and determining the total active power and the total reactive power of the variable frequency motor according to the third active power and the third reactive power of each phase.
2. The method according to claim 1, wherein the step of obtaining the corresponding phase difference change value between the input voltage and the input current of each phase of the inverter motor after adding a voltage transformer and a current transformer comprises:
acquiring each phase of third input voltage and third input current of the variable frequency motor under a rated working condition;
determining a third phase difference of a corresponding phase according to the third input voltage and the third input current of each phase;
and determining a corresponding phase difference change value according to the third phase difference.
3. The method of claim 2, wherein the step of determining from each phase second input voltage the real and imaginary parts of the fundamental vector and the real and imaginary parts of the harmonic vector of the corresponding each phase voltage comprises: for the second input voltage of each phase,
converting the second input voltage into an input voltage in the form of a Fourier series;
determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series;
the step of determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to each phase of second input current comprises the following steps: for the second input current of each phase,
converting the second input current into an input current in the form of a Fourier series;
and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
4. An inverter motor power measurement device, the device comprising:
the second input voltage acquisition module is used for acquiring second input voltage of each phase of the variable frequency motor after the voltage transformer and the current transformer are added;
the second input current acquisition module is used for acquiring second input current of each phase of the variable frequency motor after the voltage transformer and the current transformer are added;
the second input voltage determining module is used for determining the real part and the imaginary part of a fundamental wave vector and the real part and the imaginary part of a harmonic wave vector of each corresponding phase voltage according to the second input voltage of each phase;
the second input current determining module is used for determining the real part and the imaginary part of the fundamental wave vector and the real part and the imaginary part of the harmonic wave vector of each corresponding phase current according to the second input current of each phase;
the second phase power determination module is used for determining corresponding second active power and second reactive power of each phase according to the real part and the imaginary part of the fundamental wave vector of each phase voltage, the real part and the imaginary part of the harmonic wave vector, the real part and the imaginary part of the fundamental wave vector of each phase current and the real part and the imaginary part of the harmonic wave vector;
the phase difference change value determining module is used for acquiring a corresponding phase difference change value between each phase of input voltage and input current of the variable frequency motor after a voltage transformer and a current transformer are added;
the third phase power determining module is used for determining third active power and third reactive power of the corresponding phase of the actual input of the variable frequency motor according to the second active power, the second reactive power and the phase difference change value;
and the third power determination module is used for determining the total active power and the total reactive power of the variable frequency motor according to the third active power and the third reactive power of each phase.
5. The device according to claim 4, wherein the phase difference change value determination module is further configured to obtain a third input voltage and a third input current of each phase of the inverter motor under a rated working condition; determining a third phase difference of a corresponding phase according to the third input voltage and the third input current of each phase; and determining a corresponding phase difference change value according to the third phase difference.
6. The apparatus of claim 5, wherein the second input voltage determination module is further configured to, for a second input voltage for each phase, convert the second input voltage into an input voltage in the form of a Fourier series; determining real and imaginary parts of a fundamental wave vector and real and imaginary parts of a harmonic wave vector of the corresponding phase voltage by performing discrete Fourier transform on the input voltage in the form of Fourier series;
the second input current determination module is further used for converting the second input current into an input current in a Fourier series form for the second input current of each phase; and determining the real part and the imaginary part of the corresponding phase current fundamental wave vector and the real part and the imaginary part of the harmonic wave vector by performing discrete Fourier transform on the input current in the Fourier series form.
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| US5508617A (en) * | 1993-03-19 | 1996-04-16 | Hewlett-Packard Company | Electric power measuring apparatus and method |
| CN1506693A (en) * | 2002-12-09 | 2004-06-23 | 骥 卢 | Observation method of expressing leakage coefficient of asynchronous motor with fundamental variable |
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| KR101450646B1 (en) * | 2013-09-12 | 2014-10-15 | 주식회사 비츠로시스 | Method for measuring reactive power |
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| US5508617A (en) * | 1993-03-19 | 1996-04-16 | Hewlett-Packard Company | Electric power measuring apparatus and method |
| CN1506693A (en) * | 2002-12-09 | 2004-06-23 | 骥 卢 | Observation method of expressing leakage coefficient of asynchronous motor with fundamental variable |
| CN101710161A (en) * | 2009-12-25 | 2010-05-19 | 河海大学 | Rotor ground on-line monitoring device and method based on adaptive frequency square-wave voltage |
| KR101450646B1 (en) * | 2013-09-12 | 2014-10-15 | 주식회사 비츠로시스 | Method for measuring reactive power |
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