Summary of the invention
The present invention is exactly in order to overcome above deficiency, to have proposed the rotation blocking parameter recognition method and the device of a kind of high accuracy and simple asynchronous motor.
For achieving the above object, the invention provides a kind of rotation blocking parameter recognition method of asynchronous motor, may further comprise the steps:
A. make the wherein phase winding open circuit of described asynchronous motor, on two phase windings in addition of described asynchronous motor, apply the sinusoidal ac of certain frequency;
B. cross current instantaneous value on described two phase windings according to certain sampling period sample streams, test out current amplitude according to current instantaneous value;
C. when described asynchronous motor is stablized, test out the voltage magnitude between described two phase windings, and when being zero according to voltage and current instantaneous value when being zero the difference of pairing voltage-phase test out the phase difference of voltage, electric current;
D. basis
Calculate stator, the rotor resistance sum of asynchronous motor, according to
Calculate stator, rotor leakage inductance, wherein U
mBe measured voltage magnitude, I
mCurrent amplitude when stablizing for reaching described asynchronous motor on two phase windings, θ are measured voltage, the phase difference of electric current.
Preferably, the method for the described phase difference that tests out voltage, electric current is as follows: from voltage-phase is moment of 0 to begin to judge whether the current instantaneous value of being sampled is zero; And the voltage phase angle when when being, noting current instantaneous value and being zero; Calculate the phase difference of voltage, electric current by described voltage phase angle.
Further preferably, the method for the described phase difference that tests out voltage, electric current is as follows:
A), be moment of 0 to begin to judge the current instantaneous value of being sampled out from voltage-phase, when i occurring
nI
N+1<0 o'clock, i wherein
nBe the current instantaneous value of the n time sampling, i
N+1It is the current instantaneous value of the n+1 time sampling; Voltage phase angle θ when then noting the n+1 time sampling
N+1
B), pass through formula
Perhaps formula
Pairing voltage phase angle, wherein T when calculating electric current and be zero
sBe the sampling period, w is the sinusoidal current angular frequency;
Pairing voltage phase angle draws the phase difference of voltage, electric current when c), being zero by current instantaneous value.
The step that also comprises the stator resistance of testing asynchronous motor, shown in stator, rotor resistance sum deduct described stator resistance and be rotor resistance.
When the round that also comprises the steps: to work as the phase difference of the voltage that tested out, electric current between described step C and the step D reaches preset value, phase difference to all voltages, electric current is averaged, all current amplitudes are averaged, all voltage magnitudes are averaged.
Also comprise the steps: between described step C and the step D voltage magnitude to be revised by the pressure drop of compensation conduction pipe.
Described asynchronous motor is stable to be meant that the current amplitude that tests out reaches current rating.
For achieving the above object, the invention provides a kind of rotation blocking parameter recognition device of asynchronous motor, comprise that voltage provides unit, current instantaneous value sampling unit, current amplitude test cell, electric motor state judging unit, voltage magnitude test cell, voltage, current and phase difference test cell and rotation blocking parameter processing unit; The sinusoidal ac that described voltage provides the unit that certain frequency is provided on two phase windings of asynchronous motor, another phase winding open circuit of described asynchronous motor; Described current instantaneous value sampling unit is crossed the current instantaneous value on described two phase windings and is exported described current amplitude test cell to according to certain hour gap sample streams; The output triggering signal was to current amplitude test cell, voltage magnitude test cell and voltage, current and phase difference test cell when described electric motor state judgment unit judges went out motor and is in stable state; Described current amplitude test cell tests out current amplitude according to current instantaneous value, and current amplitude is exported to the rotation blocking parameter processing unit after receiving triggering signal; Described voltage magnitude test cell tests out the voltage magnitude between described two phase windings and exports the rotation blocking parameter processing unit to after receiving triggering signal; When described voltage, current and phase difference test cell receive after the triggering signal and to be zero according to voltage and electric current when being zero the difference of pairing voltage-phase test out the phase difference of voltage, electric current and export the rotation blocking parameter processing unit to; Described rotation blocking parameter processing unit is according to formula
Calculate stator, rotor resistance sum and stator, rotor leakage inductance, the wherein U of asynchronous motor
mBe the voltage magnitude between two phase windings of input, I
mCurrent amplitude on two phase windings when stablizing for described asynchronous motor, θ are the phase difference of voltage, electric current.
Preferably, described voltage, current and phase difference test cell comprise voltage-phase identification module, current instantaneous value judge module, voltage phase angle collection module and voltage, current and phase difference computing module; Described voltage-phase identification module judges whether current voltage-phase is 0, and exports first pumping signal to the current instantaneous value judge module when being; Described current instantaneous value judge module judges that whether the current instantaneous value that described current instantaneous value sampling unit is exported is zero, and export second pumping signal to the voltage phase angle collection module when being after receiving first pumping signal; Described voltage phase angle collection module receives the current voltage phase angle of the second pumping signal post-sampling, and exports described voltage, current and phase difference computing module to; Described voltage, current and phase difference computing module calculate voltage, current and phase difference according to the voltage phase angle of input.
Further preferably, described voltage, current and phase difference test cell comprise voltage-phase identification module, current instantaneous value judge module, voltage phase angle collection module, zero current corresponding phase value computing module and voltage, current and phase difference computing module; Described voltage-phase identification module judges whether current voltage-phase is 0, and exports first pumping signal to the current instantaneous value judge module when being; Described current instantaneous value judge module judges whether adjacent twice current instantaneous value of being imported by the current instantaneous value sampling unit satisfies i after receiving first pumping signal
nI
N+1<0, i wherein
nBe the current instantaneous value of the n time sampling, i
N+1Be the current instantaneous value of the n+1 time sampling, and when being, export second pumping signal to the voltage phase angle collection module; Described voltage phase angle collection module receives the voltage phase angle of collecting after second pumping signal when sampling for the n+1 time, and exports described zero current corresponding phase value computing module to; Described zero current corresponding phase value computing module is handled pairing voltage-phase value when obtaining electric current and being zero according to the voltage phase angle of input, and exports described voltage, current and phase difference computing module to; Described voltage, the current and phase difference computing module voltage phase angle during according to the input zero current calculates voltage, current and phase difference.
The beneficial effect that the present invention is compared with the prior art is: the inventive method does not need in the one-period of offset of sinusoidal electric current hundreds of even thousands of current instantaneous values to handle by fast fourier transform to obtain the active component of current and the reactive component of current, obtain phase difference between sinusoidal voltage and the sinusoidal current but directly detect sinusoidal voltage and sinusoidal current, method of the present invention do not need to a large amount of numerals handle, processing method is very simple, practical.Pairing voltage-phase value tested out the phase difference of voltage, electric current when the present invention was zero by current instantaneous value in addition, made the phase difference of measured voltage, electric current very accurate, thereby had guaranteed the accuracy of the rotation blocking parameter that picked out.
Embodiment
Also in conjunction with the accompanying drawings the present invention is described in further details below by concrete execution mode.
The present invention has disclosed a kind of precision height, the simple to operate and off-line identifying approach that can be used widely on engineering, as shown in Figure 2, the inventive method is a kind of offline parameter identifying approach that is used in the voltage-type ac-dc-ac inverter governing system, this method is based on as shown in Figure 3 motor stable state equivalent circuit, and the parameter of the knowledge of debating is the parameter in the stable state equivalent circuit.In motor stable state equivalent circuit as shown in Figure 3, comprise stator resistance r
1, stator leakage inductance L
1, rotor resistance r
2, rotor leakage inductance L
2, excitation winding equivalent resistance r
m, excitation winding equivalent inductance L
mThe field excitation branch line of forming.
Method of the present invention need pick out the rotation blocking parameter of asynchronous motor, thereby need carry out locked rotor test.Locked rotor test is short circuit test again, measures more accurately and should adopt the three-phase locked rotor test, and during the asynchronous motor stall, the impedance of field excitation branch line is far longer than the rotor loop impedance, therefore can think the field excitation branch line open circuit.Ignore iron loss, the equivalent circuit diagram during short circuit as shown in Figure 4 like this.Consider in actual applications motor is carried out relatively difficulty of stall, need to use the mechanical device fixed rotor, can not allow rotor rotation again.Adopt the single-phase short circuit test to replace three-phase test among the present invention.When motor is coupled with single-phase sinusoidal voltage, there is not electromagnetic torque to produce, basic identical when its electromagnet phenomenon and three-phase stall.Concrete grammar is: allow a certain phase (as: B phase) winding of asynchronous motor open a way, the sinusoidal ac that applies certain frequency in addition between two-phase (as: A, the C phase) winding at described asynchronous motor, the electric current that other two phase winding upper reaches are crossed reaches the rated value of described asynchronous motor, measure the phase angle difference between electric current, voltage and the voltage and current on the stator this moment, can calculate the short-circuit resistance and the leakage inductance of motor.
As shown in Figure 5, a kind of rotation blocking parameter recognition method of asynchronous motor comprises the steps:
The first step: make the phase winding open circuit of described asynchronous motor, on two phase windings in addition of described asynchronous motor, apply the sinusoidal ac of certain frequency.As shown in Figure 2, be located at making alive on A phase winding and the C phase winding, sinusoidal voltage can produce like this: the switch transistor T 3, the switch transistor T 4 that link to each other with the B phase winding are turn-offed all the time, be equivalent to make B phase winding open circuit, between 0 degree-180 degree phase places, make T1 conducting all the time, switch transistor T 2, switch transistor T 5 are turn-offed all the time, switching tube T6 is applied its conducting of pulse-triggered that pulsewidth changes by sinusoidal rule, then occur the sinusoidal voltage of positive half cycle between A phase winding and the C phase winding; Between 180 degree-360 degree phase places, make switch transistor T 2 conducting all the time, switch transistor T 1, switch transistor T 6 are turn-offed all the time, and switching tube T5 is applied pulsewidth by its conducting of pulse-triggered that sinusoidal rule changes, and then occur the sinusoidal voltage of negative half period between A phase winding and the C phase winding.When applying sinusoidal ac, should consider the influence in dead band.
Second step: cross current instantaneous value on described A phase winding or the C phase winding according to the fixed frequency sample streams, the current instantaneous value of storage one-period calculates current amplitude I
mThe computing formula of sinusoidal current fundamental voltage amplitude is:
Wherein i is the sinusoidal current instantaneous value.With this formula discretization, obtain the sinusoidal current instantaneous value of one-period, can obtain sinusoidal current fundamental voltage amplitude I
m
The 3rd step: judge whether asynchronous motor enters stable state, and whether promptly described current amplitude reaches the current rating of described asynchronous motor, if just enter next step.Can produce a fundamental frequency this moment on A phase winding or C phase winding be f, and fundamental voltage amplitude is U
mSinusoidal voltage.As shown in Figure 6, be unlikely to overcurrent in order to guarantee electric current to reach specified, can regulate the sinusoidal voltage amplitude that is carried between A phase winding and the C phase winding by a pi regulator, by the PWM control module sinusoidal ac of this specific voltage amplitude is exported to asynchronous click again, thereby finished adjusting the sinusoidal current amplitude between A phase winding and the C phase winding.Described current amplitude is that the current rating that reaches described asynchronous motor is meant that both difference get final product less than a default error, and does not require that the load current value of current amplitude and asynchronous motor is just the same.
The 4th step: the load current value that whether reaches described asynchronous motor according to current amplitude tests out the voltage magnitude between described two phase windings.As shown in Figure 6, Ie is the rated current of asynchronous motor, and Im is a current amplitude, and proportional integral (PI) adjuster generates output valve K according to Im and Ie, and this is exactly the proportionality coefficient between sinusoidal voltage fundamental voltage amplitude and the DC bus-bar voltage.Therefore, the sinusoidal voltage fundamental voltage amplitude is U just
m=KUdc, wherein Udc is a d-c bus voltage value, i.e. the voltage of 1 collector electrode of the switch transistor T among Fig. 2 and switch transistor T 2 inter-collectors.
The 5th step: when being zero according to voltage-phase and electric current when being zero the difference of pairing voltage-phase value test out the phase difference of voltage, electric current.Obvious the 5th step and the 4th step can be changed mutually.Shown in Fig. 7 a, 7b, 7c, 7d, the ideal value of phase difference is the phase difference between position 2 and the position 0 between the voltage and current.
In order to obtain the phase difference between sinusoidal voltage and the sinusoidal current, can adopt following several method:
First kind: from voltage-phase is moment of 0 to begin to judge whether the current instantaneous value of being sampled out is 0; If then note voltage phase angle θ at this moment
n, described voltage phase angle θ
nBe the phase difference of voltage, electric current.In Fig. 7 a, 7b, 7c and 7d, selecting from voltage-phase respectively is the instantaneous value that 0 moment (corresponding to position 0) began to judge sample rate current, when the instantaneous value of the electric current that occurs sampling out is 0 (corresponding to 2 places, position), write down the voltage-phase value of current time, draw the phase difference of voltage, electric current according to the voltage phase angle of current time.
Below described first method is described further, in Fig. 7 a, 7c, selection is the instantaneous value that moment (corresponding to position 0) of 0 begins to judge sample rate current from voltage-phase, in phase place is spent simultaneously less than 90 scopes of spending greater than 0, when the instantaneous value that sample rate current occurs is 0 (corresponding to 2 places, position), the voltage-phase value of record current time deducts 0 phase difference that can draw between sinusoidal voltage and the sinusoidal current with the voltage-phase value of current time.In Fig. 7 b, 7d, selection is the instantaneous value that moment (corresponding to position 0) of 0 begins to judge sample rate current from voltage-phase, in phase place is spent simultaneously less than 270 scopes of spending greater than 180, when the instantaneous value that sample rate current occurs be 0 (corresponding to 2 places, position) constantly, the voltage-phase value of record current time deducts 180 with the voltage-phase value of current time and spends the phase difference that can draw between sinusoidal voltage and the sinusoidal current.
Because current instantaneous value is sampled by discrete way, and discrete way meeting generation time at interval, and then can to cause sampled result be interrupted rather than continuous, this will cause in most cases, the current instantaneous value that is difficult to occur sampling just equals the situation of 0 (the just 2 places sampling in the position), and this moment, the user just can select for use second method to obtain phase difference between sinusoidal voltage and the sinusoidal current.
Second kind: shown in Fig. 7 a, 7b, 7c, 7d,, can realize by the current instantaneous value at
detection position 1 and 3 places, position in order to detect the phase difference between the voltage and current.That is: be moment of 0 to begin to judge the current instantaneous value of being sampled out from voltage-phase, when i occurring
nI
N+1<0, i wherein
nBe the current instantaneous value of the n time sampling, i
N+1Be the current instantaneous value of the n+1 time sampling, the voltage phase angle θ at (corresponding to 3 places, position) when then noting the n+1 time sampling
N+1Pass through formula
Perhaps formula
Pairing voltage-phase value, wherein T when calculating current instantaneous value and be zero
sBe the sampling period, w is the sinusoidal current angular frequency, and θ is the phase difference of voltage, electric current; Pairing voltage-phase is worth the phase difference of voltage, electric current when being zero by current instantaneous value.
Below described second method is described further, in Fig. 7 a, 7c, selecting from voltage-phase is the instantaneous value that moment (corresponding to position 0) of 0 begins to judge sample rate current, in phase place greater than 0 degree simultaneously in the scopes less than 90 degree, when i occurring
nI
N+1<0 (comprises the i among Fig. 7 a
n<0, i
N+1>0 and Fig. 7 c in i
n>0, i
N+1<0) time, i wherein
nBe the current instantaneous value of the n time sampling, i
N+1The current instantaneous value at (corresponding to 3 places, position) when being the n+1 time sampling, the voltage phase angle θ when then noting the n+1 time sampling
N+1In Fig. 7 b, 7d, selecting from voltage-phase is the instantaneous value that moment (corresponding to position 0) of 0 begins to judge sample rate current, in phase place greater than 180 degree simultaneously in the scopes less than 270 degree, when i occurring
nI
N+1<0 (comprises the i among Fig. 7 b
n<0, i
N+1>0 and Fig. 7 d in i
n>0, i
N+1<0) time, the voltage phase angle θ when then noting the n+1 time sampling
N+1If the sampling period is T
s, then the phase place between position 1 and the position 3 is crossed over and is Δ θ
3-1=wT
s, wherein w is the sinusoidal current angular frequency.Above-mentioned voltage-phase is that 0 moment user can set as required, can choose to get final product from voltage is 0 point.
Because the sampling period is very short, all is the microsecond level generally, therefore, for a current cycle, can think that from the position 13 is approximately linear transition to the position, thereby can think that the position 2 of expection and phase place leap between the actual position 3 are
Δ θ wherein
3-2Be the phase difference between position 3 and the position 2, Δ θ
3-1Be the phase difference between position 3 and the position 1, this formula all is suitable for Fig. 7 a, 7b, four kinds of situations of 7c, 7d.
Therefore, the phase difference between revised sinusoidal voltage and the sinusoidal current is:
For Fig. 7 a and 7c both of these case,
For Fig. 7 b and 7d both of these case,
Wherein, θ is the phase difference of voltage, electric current.
The 6th step: in order to reduce error, can obtain phase differences between many group sinusoidal voltages and the sinusoidal current by the method for repeatedly averaging, averaged then, and the input of these mean values as the 7th step formula.At this moment can also average as the input of the 7th step formula organizing corresponding sinusoidal current amplitude, sinusoidal voltage amplitude with these, perhaps will last sinusoidal current amplitude, the sinusoidal voltage amplitude is as the 7th input that goes on foot formula.
After the 5th step, judge the obtaining round and whether reach preset value of phase difference of voltage, electric current, if the phase difference between sinusoidal current amplitude, sinusoidal voltage amplitude and the sinusoidal voltage and the sinusoidal current of these rounds is averaged and as the 7th input that goes on foot formula; If add 1 and return the first step otherwise will obtain round.
Obviously, the user also can be as required, respectively in three phase windings of asynchronous motor each in twos combined situation all test, ask for the mean value of the phase difference between sinusoidal current amplitude, sinusoidal voltage amplitude and sinusoidal voltage and the sinusoidal current.Described the 6th the step can be seen as a preferred step, promptly by the 5th the step directly enter the 7th the step also be fine.
The 7th step: according to the sinusoidal current amplitude I that is obtained
m, sinusoidal voltage amplitude U
mWith electric current and voltage phase difference θ, and the influence of conduction pipe pressure drop in the detailed consideration vector control system, according to formula
Just can be regarded as the resistance sum of stator, rotor of asynchronous motor and stator, rotor leakage inductance, wherein U
mVoltage magnitude between two phase windings when being in stable state for asynchronous motor, I
mCurrent amplitude on two phase windings when being in stable state for asynchronous motor, θ is the voltage of asynchronous motor when being in stable state, the phase difference of electric current, R is the stator of asynchronous motor, the resistance sum of rotor, and X is stator, the rotor leakage inductance of asynchronous motor.
Consider the influence of conduction pipe pressure drop, we can offset of sinusoidal voltage magnitude U
mRevise, establishing revised voltage magnitude is U
M11, then the resistance sum of stator, rotor is:
Stator, rotor leakage inductance are
The concrete modification method of voltage magnitude has been a mature technique, and the present invention repeats no more.
Before the stall identification, can test out the stator resistance of asynchronous motor earlier, shown in stator, rotor resistance sum deduct described stator resistance and be rotor resistance.Because the stator resistance of test asynchronous motor is a kind of mature technique, so repeat no more herein.
Rotor resistance resistance and closely related as can be seen from this step with the electric current and voltage phase difference, the result of stall identification depends on the electric current and voltage value and the electric current and voltage phase difference of sampling to a great extent, therefore, the extraction of electric current and voltage phase difference must be accurate as far as possible, otherwise it is big or suddenly little that the rotor resistance that may cause stall to pick out is neglected, and cause the instability of stall identification result, method of the present invention can realize the accurate extraction to the electric current and voltage phase difference, thereby guarantee the stability of the identification result of the inventive method, and then guarantee vector control system controlled of asynchronous motor.
Below by a contrast experiment effect of the present invention is described further: use method of the present invention that rated power has been carried out the parameter identification test as the motor of 15KW, and, carried out the open loop vector operation of 15KW asynchronous motor directly according to the motor parameter that picks out.Table 1 has been listed the nameplate parameter of this asynchronous motor.
Model |
Rated power |
Rated voltage |
Rated current |
Rated frequency |
Rated speed |
1LA7166-4AA61 |
15KW |
380V |
29.5A |
50.00Hz |
1460r/min |
Table 1
Table 2 has provided the present invention and the prior art identification result to the asynchronous motor rotation blocking parameter.
Table 2
Adopt the present invention that asynchronous motor has been carried out the stall identification, the stall identification is carried out the open loop vector to the 15KW asynchronous motor and is run to 50Hz after finishing, and the rotating speed stable state accuracy that records rotor is less than ± 3 rev/mins.
Adopt prior art that asynchronous motor has been carried out the stall identification, after identification finishes, the 15KW asynchronous motor is carried out the open loop vector run to 50Hz, in six groups of parameters, have only two groups of motor parameters can guarantee that open loop vector operation has reached the rotating speed stable state accuracy less than ± 3 rev/mins, all the other four groups of motor parameters cause the rotating speed stable state accuracy all surpass ± 3 rev/mins.Obviously, prior art in most of the cases can't guarantee control performance.
As can be seen from Table 2, the rotor resistance resistance drift that prior art picks out is very big, and the twice identification result deviation in front and back substantially all surpasses 5% (deviation of having only the 2nd time and the 3rd time this adjacent twice identification result is less than 5%).And the rotor resistance resistance that the present invention picks out drift is very little, and the twice identification result deviation in front and back is all less than 1.5%.Therefore, the present invention is being significantly increased aspect identification result stability and the assurance control performance with respect to prior art.
As shown in Figure 8, a kind of rotation blocking parameter recognition device of asynchronous motor comprises that voltage provides unit, current instantaneous value sampling unit, current amplitude test cell, electric motor state judging unit, voltage magnitude test cell, voltage, current and phase difference test cell and rotation blocking parameter processing unit; The sinusoidal ac that described voltage provides the unit that certain frequency is provided on two phase windings of asynchronous motor, another phase winding open circuit of described asynchronous motor; Described current instantaneous value sampling unit is crossed the current instantaneous value on described two phase windings and is exported described current amplitude test cell to according to certain sampling period sample streams; The output triggering signal was to current amplitude test cell, voltage magnitude test cell and voltage, current and phase difference test cell when described electric motor state judgment unit judges went out motor and is in stable state; Described current amplitude test cell tests out current amplitude according to current instantaneous value, and current amplitude is exported to the rotation blocking parameter processing unit after receiving triggering signal; Described voltage magnitude test cell tests out the voltage magnitude between described two phase windings and exports the rotation blocking parameter processing unit to after receiving triggering signal; When described voltage, current and phase difference test cell receive after the triggering signal and to be zero according to voltage and current instantaneous value when being zero the difference of pairing voltage-phase test out the phase difference of voltage, electric current and export the rotation blocking parameter processing unit to; Described rotation blocking parameter processing unit is according to formula
Calculate stator, rotor resistance sum and stator, rotor leakage inductance, the wherein U of asynchronous motor
mBe the voltage magnitude between two phase windings of input, I
mCurrent amplitude on two phase windings when stablizing for described asynchronous motor, θ are the phase difference of voltage, electric current.
Described voltage, current and phase difference test cell can adopt following mode to realize: described voltage, current and phase difference test cell comprise voltage-phase identification module, current instantaneous value judge module, voltage phase angle collection module and voltage, current and phase difference computing module; Described voltage-phase identification module judges whether current voltage-phase is 0, and exports first pumping signal to the current instantaneous value judge module when being; Described current instantaneous value judge module judges that whether the current instantaneous value that described current instantaneous value sampling unit is exported is zero, and export second pumping signal to the voltage phase angle collection module when being after receiving first pumping signal; Described voltage phase angle collection module receives the current voltage phase angle of the second pumping signal post-sampling, and exports described voltage, current and phase difference computing module to; Described voltage, current and phase difference computing module calculate voltage, current and phase difference according to the voltage phase angle of input.
Described voltage, current and phase difference test cell comprise voltage-phase identification module, current instantaneous value judge module, voltage phase angle collection module, zero current corresponding phase value computing module and voltage, current and phase difference computing module; Described voltage-phase identification module judges whether current voltage-phase is 0, and exports first pumping signal to the current instantaneous value judge module when being; Described current instantaneous value judge module judges whether adjacent twice current instantaneous value of being imported by the current instantaneous value sampling unit satisfies i after receiving first pumping signal
nI
N+1<0, i wherein
nBe the current instantaneous value of the n time sampling, i
N+1Be the current instantaneous value of the n+1 time sampling, and when being, export second pumping signal to the voltage phase angle collection module; Described voltage phase angle collection module receives the voltage phase angle of collecting after second pumping signal when sampling for the n+1 time, and exports described zero current corresponding phase value computing module to; Described zero current corresponding phase value computing module is handled pairing voltage-phase value when obtaining electric current and being zero according to the voltage phase angle of input, and exports described voltage, current and phase difference computing module to; Described voltage, the current and phase difference computing module voltage phase angle during according to the input zero current calculates voltage, current and phase difference.
Above content be in conjunction with concrete preferred implementation to further describing that the present invention did, can not assert that concrete enforcement of the present invention is confined to these explanations.For the general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, the some simple deduction or replace of being made all should be considered as belonging to protection scope of the present invention.