The method of tracing motor rotation speed by frequency transformer and device thereof
Technical field
The present invention relates to the rotating-speed tracking method, more particularly, relate to a kind of method and device of tracing motor rotation speed by frequency transformer.
Background technology
Frequency converter is a kind of equipment that drives alternating current motor, in the application of industrial circle more and more widely in recent years.The extensive use of frequency converter not only can improve the level of China's equipment manufacture, also can reach obviously energy-conservation effect in some industry.
Before the operation of frequency converter drive motors, motor might be in rotation status, and for example blower fan may be with no small rotating speed rotation under the effect of ambient wind power; Perhaps occur electrical network suddenly when frequency converter drive motors high-speed cruising and fall, frequency converter is because under-voltage and lose control to motor, thereby motor high speed rotating under action of inertia occurs.If motor is in rotation status, then frequency converter must obtain rotating speed of motor earlier, just can normally control motor then, otherwise overcurrent, overvoltage fault alarm can appear in frequency converter, perhaps damages motor because of frequency converter is in the stall over-current state for a long time.
Rotating-speed tracking just is meant that frequency converter before the beginning drive motors, detects the actual speed of motor earlier automatically, and the method for this detection motor speed is called the rotating-speed tracking method.
On the technical literature and market product of the current industry, the method for following several rotating-speed trackings is arranged:
A, utilize the dc bus current method
The size of frequency changer direct current bus electric current can reflect the size of motor output torque, and when motor output torque was 0, the electric current on the frequency changer direct current bus was 0.Utilize this characteristics, frequency converter does not stop to revise output frequency in the rotating-speed tracking process, and when the frequency converter output frequency was identical with motor speed, motor output torque should be 0, and can embody on the bus current this moment.
This method specific implementation method is: adopt closed loop controller closed-loop control direct current, given electric current is 0, and then closed loop controller is output as the frequency converter output frequency, and the frequency converter output frequency under the closed-loop control stable state is exactly the actual speed of motor.
This method is not easy to realize that two main problems are on product:
One, on the frequency changer direct current bus electric current very big current ripples is arranged, this ripple makes judges that whether dc bus current is 0 is a very difficult technology.Two, generally have only the three-phase output current to detect in the frequency converter, do not have current sensing means on the dc bus, adopt this method of realization need increase by a cover current sensing means, the cost of increase, and reduced reliability of products.
B, utilize hardware circuit, detect the method for counter electromotive force of motor
This method main thought is to utilize the back electromotive force of motor to detect rotating speed of motor, and this method is to utilize special hardware circuit to detect the back electromotive force of motor, and the frequency of back electromotive force promptly is the motor speed frequency.
The major defect of this method is to need special hardware circuit, and this circuit has not only increased cost in commercialization, also reduced the reliability of system.
Summary of the invention
The technical problem to be solved in the present invention is, at the above-mentioned defective of prior art, provides a kind of method and device of tracing motor rotation speed by frequency transformer.
The technical solution adopted for the present invention to solve the technical problems is: construct a kind of method of tracing motor rotation speed by frequency transformer, comprise the steps:
The electric current of a, control of conversion device output setpoint frequency, the amplitude of described output current is fixed;
B, according to the output frequency of frequency converter, calculate the magnitude of voltage of the V/F curve of motor;
C, judge frequency converter output voltage whether more than or equal to the magnitude of voltage of the V/F curve of described motor, in this way, enter steps d, otherwise, enter step e;
The output voltage and the output frequency of d, maintenance frequency converter are constant, finish to follow the tracks of;
E, change described setpoint frequency, and execution in step a.
In a preferred embodiment, further comprise among the described step e:
E1, judge whether the busbar voltage of frequency converter rises, if, execution in step e2; Otherwise execution in step e3;
E2, described setpoint frequency is changed fast and execution in step a;
E3, change described setpoint frequency with normal speed, and execution in step a.
In another preferred embodiment, the initial value of described setpoint frequency is 0Hz, further comprises among the described step e:
E1 ', judge whether described setpoint frequency is the frequency converter peak frequency, if, execution in step e3 ' then; Otherwise execution in step e2 ';
E2 ', described setpoint frequency is risen, and execution in step a;
E3 ', end search.
In a preferred embodiment again, the initial value of described setpoint frequency is the shutdown frequency of a frequency converter peak frequency or a preceding frequency converter, further comprises among the described step e:
E1 ", judge whether described setpoint frequency is 0Hz, if, execution in step e3 then "; Otherwise execution in step e2 ";
E2 ", described setpoint frequency is descended, and execution in step a;
E3 ", finish search.
In the method for tracing motor rotation speed by frequency transformer of the present invention, in step b,, handle with 0Hz if when the output frequency of described frequency converter is 0~5Hz.
In the method for tracing motor rotation speed by frequency transformer of the present invention, the amplitude of the output current of described frequency converter equates with the amplitude of the rated current of described motor.
The present invention further provides a kind of device of tracing motor rotation speed by frequency transformer, comprising:
Be used for the first control device of control of conversion device output setpoint frequency electric current, the amplitude of described output current is fixed;
Be used for output frequency, the arithmetic unit of the magnitude of voltage of the V/F curve of calculating motor according to frequency converter;
Be used for first comparison means that the magnitude of voltage with the V/F curve of the output voltage of frequency converter and described motor compares;
Be used for when described comparison means determines that the magnitude of voltage of frequency converter output voltage and the V/F curve of motor is identical, keep output voltage and output frequency is constant and the second control device that finishes to follow the tracks of;
Be used for determining that at described comparison means the magnitude of voltage of the V/F curve of frequency converter output voltage and motor does not change the converter plant of described setpoint frequency simultaneously.
In a preferred embodiment, described converter plant comprises:
Be used to judge first the comparator whether busbar voltage of frequency converter rises;
Be used for when described first comparator determines that the frequency converter busbar voltage rises, making fast-changing first frequency converter of described setpoint frequency;
Be used for when described first comparator determines that the frequency converter busbar voltage does not rise, changing second frequency converter of described setpoint frequency with normal speed.
In another preferred embodiment, the initial value of described setpoint frequency is 0Hz, and described converter plant comprises:
Be used to judge whether described setpoint frequency is second comparator of frequency converter peak frequency;
Be used for when described second comparator is confirmed setpoint frequency non-frequency device peak frequency the 3rd frequency converter that described setpoint frequency is risen.
In a preferred embodiment again, the initial value of described setpoint frequency is the shutdown frequency of a frequency converter peak frequency or a preceding frequency converter, and described converter plant comprises:
Be used to judge whether described setpoint frequency is the 3rd comparator of 0Hz;
Be used for when described the 3rd comparator confirms that setpoint frequency is not equal to 0Hz the 4th frequency converter that described setpoint frequency is descended.
Implement the method for tracing motor rotation speed by frequency transformer of the present invention, has following beneficial effect: with the method contrast of adopting the hardware detection back electromotive force, this method has been omitted the cost of rotating-speed tracking circuit, and the system failure point of having avoided above-mentioned hardware circuit to bring, improved the reliability of system, made system on cost and reliability, all have remarkable advantages.Comparing this method with the method that adopts bus current has two advantages, and the one, saved the testing circuit of bus current, save cost and improved reliability.The 2nd, the better effects if that speed is followed the tracks of has improved the performance of system.
Description of drawings
The invention will be further described below in conjunction with drawings and Examples, in the accompanying drawing:
Fig. 1 is the flow chart of the method for tracing motor rotation speed by frequency transformer of the present invention;
Fig. 2 is a preferred embodiment flow chart that changes the setpoint frequency step among Fig. 1;
Fig. 3 is another preferred embodiment flow chart that changes the setpoint frequency step among Fig. 1;
Fig. 4 is a preferred embodiment flow chart again that changes the setpoint frequency step among Fig. 1.
Embodiment
The present invention utilizes counter electromotive force of motor to carry out rotating-speed tracking, basic ideas are that frequency converter is exported different frequency but the fixing electric current of amplitude, frequency converter must constantly be regulated the magnitude of voltage of being exported for this reason, and when motor speed and frequency converter output current frequency at once, frequency converter output voltage is consistent with the V/F nominal parameter of motor, whether has exported correct voltage according to frequency converter and can judge whether the power frequency of present output is consistent with motor speed.
The present invention (perhaps drops to 0 from peak frequency gradually by the frequency converter output frequency is increased to peak frequency gradually from 0Hz; perhaps shut down frequency and drop to 0 gradually) from the frequency converter of last time; utilizing closed loop controller (for example PID adjuster) closed-loop control frequency converter output current in this process is the motor rated current; closed loop is output as the size of frequency converter output voltage; judge then whether this output voltage is consistent with the V/F curve of motor, when both are consistent, think that motor speed is consistent with the frequency converter output frequency.
In the method for a kind of tracing motor rotation speed by frequency transformer shown in Figure 1, comprise the steps:
The electric current of S11, control of conversion device output setpoint frequency, the amplitude of above-mentioned output current is fixed.
In this step, frequency converter is by regulating the size of the magnitude of voltage change output current of being exported.Theoretically, frequency converter output current (being the amplitude of above-mentioned setting electric current) is identical with the motor load current amplitude best, but because the load current amplitude is unknowable, so in actual applications, the amplitude of frequency converter output current adopts motor rated current amplitude.
S12, according to the output frequency of frequency converter, calculate the magnitude of voltage of the V/F curve of motor.The V/F curve of motor is set by the function code of frequency converter, and according to the voltage of motor under this curve calculation different frequency, the voltage-contrast of this voltage and closed loop controller is if this voltage, thinks then that motor speed is exactly the output frequency of current frequency converter smaller or equal to the voltage of closed loop controller.
S13, judge frequency converter output voltage whether more than or equal to the magnitude of voltage of the V/F curve of described motor, in this way, enter step S14, otherwise, enter step S15.
The output voltage and the output frequency of S14, maintenance frequency converter are constant, and frequency converter output frequency at this moment as motor speed, is finished to follow the tracks of.
In practical operation, may there be deviation in the motor speed that said method obtains, and the size of deviation is relevant with the actual speed of pair value, frequency change speed and the motor of frequency converter output current.The existence of velocity deviation can make system warnings such as overcurrent or overvoltage occur in transient process, so should avoid as far as possible.At this problem: after search finishes, need to increase a transient process, guarantee that motor is smoothly transitted into the Frequency Converter Control running status.This transient process is and keeps the output voltage and the output frequency of frequency converter constant, and the effect of cancellation current closed-loop controller.
S15, change described setpoint frequency, and execution in step S11.The frequency converter output frequency is increased to peak frequency (perhaps drop to 0 gradually from peak frequency, perhaps shut down frequency from the frequency converter of last time and drop to 0 gradually) gradually from 0Hz.
When specific implementation, the setpoint frequency of Frequency Converter Control electric current carries out conversion by the speed of 10Hz/ second.Certain above-mentioned conversion rate also can be adjusted according to actual needs, and conversion is slow more, and precision is high more.
When realizing said method of the present invention, can adopt the TMS320F240X series DSP chip of TI company, main control CPU as frequency converter, adopt current sensor senses two-phase output current, and calculate the third phase electric current, utilize three-phase current to calculate the synthetic effective value of frequency converter output current.Utilize pi regulator as the current closed-loop adjuster, current reference value is selected the motor rated current, if but the frequency converter rated current is less than the motor rated current, then select electric current that the frequency converter maximum can export for a long time as current reference value, the composite value of three-phase current is as feedback, and closed loop controller is output as frequency converter output voltage.
In the frequency of frequency converter output current during near motor speed, because required voltage sharply rises, and actual closed loop controller may not satisfy this requirement, cause actual motor current less than setting electric current, this moment stop frequency variation, wait electric current to rise to set the adjustment of carrying out output frequency behind the electric current again.On above-mentioned thinking basis, adopt search thinking first quick and back slow, can make the effect of current regulator very good.In the preferred embodiment as shown in Figure 2, further comprise among the described step S15:
S21, judge whether the busbar voltage of frequency converter rises, if, execution in step S23; Otherwise execution in step S22;
S22, described setpoint frequency is changed fast and execution in step S11, this moment, the rate of change of frequency values can be chosen as about 3 times of normal variation rate;
S23, change described setpoint frequency with normal speed, and execution in step S11.
Because frequency converter output voltage is influenced by stator resistance, therefore when the motor low cruise, the resultant error of acquisition is very big.For addressing the above problem, may command frequency converter output frequency begins to frequency converter peak frequency (perhaps drop to 4Hz gradually from peak frequency, perhaps shut down frequency from the frequency converter of last time and drop to 4Hz gradually) from 4Hz.
In another preferred embodiment as shown in Figure 3, the initial value of described setpoint frequency is 4Hz, further comprises among the described step S15:
S31, judge whether described setpoint frequency is the frequency converter peak frequency, if, execution in step S33 then; Otherwise execution in step S32;
S32, described setpoint frequency is risen, and execution in step S11;
S33, end search.
In the preferred embodiment more as shown in Figure 4, the initial value of described setpoint frequency is the shutdown frequency of a frequency converter peak frequency or a preceding frequency converter, further comprises among the described step S15:
S41, judge whether described setpoint frequency is 4Hz, if, execution in step S43 then; Otherwise execution in step S42;
S42, described setpoint frequency is descended, and execution in step S11;
S43, end search.
In addition, for avoiding the influence of low frequency stator resistance, also can be when calculating the V/F curve magnitude of voltage of motor, handle being used as 0HZ below the 5HZ, be provided with by parameter identification or user function sign indicating number simultaneously, frequency converter can obtain stator resistance occurrence (this value is unnecessary accurately), thereby when considering VF curve voltage, in the output voltage of closed loop controller the voltage drop on the stator resistance is removed.
The present invention further provides a kind of device of tracing motor rotation speed by frequency transformer, comprising: be used for the first control device of control of conversion device output setpoint frequency electric current, the amplitude of described output current is fixed; Be used for output frequency, the arithmetic unit of the magnitude of voltage of the V/F curve of calculating motor according to frequency converter; Be used for first comparison means that the magnitude of voltage with the V/F curve of the output voltage of frequency converter and described motor compares; Be used for when described comparison means determines that the magnitude of voltage of frequency converter output voltage and the V/F curve of motor is identical, keep output voltage and output frequency is constant and the second control device that finishes to follow the tracks of; Be used for determining that at described comparison means the magnitude of voltage of the V/F curve of frequency converter output voltage and motor does not change the converter plant of described setpoint frequency simultaneously.
In a preferred embodiment, described converter plant comprises: be used to judge first the comparator whether busbar voltage of frequency converter rises; Be used for when described first comparator determines that the frequency converter busbar voltage rises, making fast-changing first frequency converter of described setpoint frequency; Be used for when described first comparator determines that the frequency converter busbar voltage does not rise, changing second frequency converter of described setpoint frequency with normal speed.
In another preferred embodiment, the initial value of described setpoint frequency is 4Hz, and described converter plant comprises: be used to judge whether described setpoint frequency is second comparator of frequency converter peak frequency; Be used for when described second comparator is confirmed setpoint frequency non-frequency device peak frequency the 3rd frequency converter that described setpoint frequency is risen.
In a preferred embodiment again, the initial value of described setpoint frequency is the shutdown frequency of a frequency converter peak frequency or a preceding frequency converter, and described converter plant comprises: be used to judge whether described setpoint frequency is the 3rd comparator of 4Hz; Be used for when described the 3rd comparator confirms that setpoint frequency is not equal to 4Hz the 4th frequency converter that described setpoint frequency is descended.
The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.