JPH11164565A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a beating phenomenon of an inverter caused by a ripple component of rectified voltage of a converter, by detecting a ripple of DC input voltage of the inverter, and adjusting a pulse width of the output voltage of the inverter according to the detected ripple. SOLUTION: In a power converter wherein AC from an AC power supply 1 is inputted to a pulse width modulation inverter 4 through a converter 2 and a filter capacitor 3 and then is converted into AC of variable voltage and variable frequency and is outputted to an induction motor 5, a means 14 for adjusting the output frequency of the inverter is installed. And, a degree of a voltage ripple ΔE0 /E0 of the input voltage E of the inverter 4 is found, and then the aΔE0 /E0 is multiplied by a reference command value f0 of the output frequency by means of a multiplication means 144 to obtain an adjustment Δf0 to the output frequency and then a frequency command value 'f' is obtained from an adding means 15 and it is inputted to a modulating means 7. Then, the modulation means 7 generates a PWM modulation signal based on the frequency command value 'f' and controls the operation of a control switching element of the inverter 4 through a gate signal processing circuit 6 by the PWM modulation signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, and more particularly, to a converter and a DC output voltage thereof.
The present invention relates to an AC-AC power conversion device including an inverter that converts AC into a variable voltage and a variable frequency.

[0002]

2. Description of the Related Art Conventionally, as this type of control technique, Japanese Patent Publication No. 48356/1986 has been known. Tokiko Sho 61-48
No. 356 discloses that when a forward converter (converter) converts an alternating current into a direct current and feeds the power to a variable-voltage / variable-frequency pulse width modulation inverter, the output voltage of the forward converter, that is, the input voltage of the inverter, has a pulsating component. (Rectifier ripple), the output voltage of the inverter pulsates, especially at a certain point where the output frequency of the inverter causes a beat phenomenon. As a solution to this problem, the output voltage of the inverter does not fluctuate. A control method for adjusting an amplitude ratio of a sine wave signal and a triangular wave carrier signal, that is, a pulse width of a PWM signal, according to a change in an input voltage of an inverter is shown.

Further, Japanese Patent Application Laid-Open No. 57-52383 discloses a control for adjusting a pulse width of a PWM signal in accordance with a change in input voltage by using a pulse processing technique in order to achieve the same object. A scheme is disclosed.

[0004]

However, in these control systems, the output voltage of the inverter is maximum and the voltage cannot be controlled, for example, the number of pulses included in a half cycle of the output voltage of the PWM inverter is one pulse. In addition, there is a problem that it cannot be applied in the maximum constant voltage region.

An object of the present invention is to provide a power converter capable of suppressing a beat phenomenon of an inverter caused by a pulsation component included in a converter output voltage, that is, an inverter input voltage.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a converter for converting AC to DC, a smoothing capacitor for smoothing DC rectified by the converter, and an inverter for converting the smoothed DC to three-phase AC. A constant voltage variable frequency (CVVF) control means for variably controlling the frequency of a voltage pulse having one pulse included in a half cycle of the output voltage of the inverter at least in a region where the output voltage of the inverter is maximum and cannot be controlled. In the power converter, means for detecting a pulsation of the DC input voltage of the inverter due to rectification of the converter, and in response to the pulsation, the output of the inverter when the DC input voltage of the inverter is increased by the pulsation. When the pulse width of the voltage is narrowed and the pulsation reduces the DC input voltage of the inverter, It is achieved by providing a means for adjusting widening the pulse width of the inverter output voltage.

According to the present invention, the time width (period) of the voltage pulse for each half cycle is adjusted in the one-pulse mode CVVF control region where the output voltage of the inverter is maximized in accordance with the pulsation of the input voltage of the inverter. You. Therefore, the imbalance of the voltage-time product of the inverter output voltage for each positive and negative half cycle is compensated, and the beat phenomenon is suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit configuration of a control device for an induction motor using a converter / inverter according to an embodiment of the present invention, wherein 1 is an AC power supply, and 2 is a converter for converting the AC power supply 1 to DC. Reference numeral 3 denotes a filter capacitor for smoothing a DC voltage. Reference numeral 4 denotes a control switching element UP to WN such as a GTO thyristor, and a variable voltage / variable frequency pulse width modulation inverter for converting DC into AC. Reference numeral 5 denotes an induction motor energized by the inverter 4. Numeral 7 denotes a modulating means comprising a carrier wave generating means 71, a modulating wave generating means 72, a comparing means 73 and a pulse number switching means 74. 4 to perform on / off operations of the control switching elements UP to WN.

In FIG. 1, a rotation frequency f _n of an induction motor 5 is detected by a detection means 8 and a slip frequency command f
_S is added by the adding / subtracting means 9 during power running, and is subtracted during regeneration. This is the reference command f for the output frequency of the inverter 4.
₀ (= f _n ± f _S ). The slip frequency command f _S is obtained by comparing the value I _M of the current of the induction motor 5 detected by the detection means 10 with the command value I _P by the comparison means 11,
It is provided through the slip frequency control means 12.

On the other hand, the PWM modulation means 7, as the output frequency command f of the inverter 4, if the output f ₀ of subtraction means 9 which is a reference command is given, the modulated wave generating means 72 Fig 2 (A) As shown in (b), (c), and (d), sine waves of U, V, and W phases are generated.
1 generates the triangular wave shown in FIG. The triangular wave and the sine wave are compared by the comparing means 73, and FIG.
And outputs pulses for the control switching elements UP, VP, and WP. It should be noted that the inverted one of FIG. 2B is the pulse for the negative control switching elements UN, VN, WN.

The output voltage of the inverter 4 obtained in this manner is controlled by pulse width modulation (PWM) as shown in FIG.
It was done. Here, the input voltage E of the inverter 4
Is the DC component E ₀ without the pulsation component ΔE _0, the waveform of the output voltage (between U and V) of the inverter 4 always has a constant peak value as shown in FIG. No imbalance occurs between cycles. Then, the peak value of the sine wave in FIG. 2A is changed so that the output voltage of the inverter 4 is controlled by changing the width θ _C in FIG. 2B.

In addition, the inverter 4 included in the half cycle
The number of output voltage pulses (3 pulses in FIG. 2C) is
Triangular wave (a) and sine wave (b), (c), (d) in FIG.
Is controlled by switching the frequency of the triangular wave by the pulse number switching means 74 so as to switch the frequency ratio. This pulse number N _P is a reference command f for the output frequency f of the inverter 4.
_In response to the output of the addition / subtraction means 9 which is ₀ , the pulse number switching means 74 outputs, for example, 27-15-9- as shown in FIG.
Switch to 5-3-1. Further, the output voltage V _M of the inverter 4, the output frequency f of the inverter 4 (reference command f _0), is controlled as shown in FIG. In other words, when the frequency is _f01 or less, the variable voltage / variable frequency (VVVF) control is performed so that the output voltage of the inverter is proportional to the output frequency, and when the frequency is _f01 or more, the output voltage is fixed to a constant value. Frequency (CVVF) control is performed. This VV
In the VF control region, the voltage control means 13
And calculating a ratio, i.e. the modulation index of the peak value and the triangular wave crest value of the sine wave γ of (A), and controls the peak value of the sine wave _{(G U, G V, G} W in FIG. 2). The pulse number when the switches from 3 pulses to one pulse, the output voltage V _M of the inverter 4 is jumping. This is because the control switching elements UP to WN require a certain amount of time to extinguish the arc, so that the width θ in FIG.
The _C to 0, that is, the output voltage V _M of the inverter 4 can not be controlled continuously until one pulse having a maximum.

By the way, even if a filter capacitor 3 for smoothing a DC voltage is provided on the output side of the converter 2, the pulsation Δ
E ₀ occurs. The pulsation ΔE ₀ decreases as the capacity of the filter capacitor 3 increases, but cannot be completely removed. Further, there is a problem that the filter capacitor 3 becomes large. Therefore, the relationship of the pulsating component Delta] E ₀ in consideration inverter 4 of the input voltage E (= direct current component E ₀ + ripple component Delta] E ₀₎ and the output voltage (line-to-line) V _M, it CVVF region (the number of pulses of FIG 1 FIG. 4 shows a pulse, that is, a modulation rate γ ≧ 1 in FIG. 2A. FIG. 4 (A)
Is the frequency f _e of the pulsating component ΔE ₀ (this is constant because it is caused by the rectifying ripple). In the case of the output f ₀ of the addition / subtraction means 9,
FIG. 4C shows the frequency f _e of the pulsation ΔE ₀ ≪the addition / subtraction means 9.
Shall apply in the case of the output f _0, the output voltage of both of the inverters 4, imbalance hardly occurs between the positive and negative of each half-cycle. It should be noted that the frequency f _e of the pulsation ΔE ₀指令 the inverter command f ₀ satisfies the low-speed range, and the number of pulses is usually large as can be seen from FIG. Even in this case, it can be easily inferred from FIG. 4A that no imbalance occurs between the positive and negative half cycles of the inverter output voltage.

FIG. 4B shows an inverter frequency command f _0.
Is close to the rectified ripple frequency f _e , that is,
In the case of “frequency f _e of pulsation component ΔE ₀ ≒ inverter frequency f (= frequency reference command f ₀ )”, the inverter output voltage (voltage / time product) changes between positive and negative half cycles. A balance occurs. This situation is shown in FIGS. 4B and 4B. The magnitude of this imbalance is the pulsation ΔE ₀
Change in frequency of the difference between the output frequency f of the frequency f _e and the inverter 4, i.e. the output voltage of the inverter 4 is caused to beat phenomenon.

Therefore, in the present embodiment, as will be described below, the operating frequency pulsation degree of the inverter is adjusted in accordance with the pulsation degree based on the rectification ripple, thereby suppressing the occurrence of the imbalance and suppressing the beat reduction. .

First, the DC component E ₀ of the inverter input voltage E
Is detected by the detection means 142, and the pulsation ΔE ₀ of the input voltage E of the inverter 4 is detected by the detection means 141 with a predetermined phase difference α. The output Δ of this detection means 141
E ₀ ′ (the phase is different when | ΔE ₀ ′ | = | ΔE ₀ |) is divided by the divider E 143 with the output E ₀ of the detector 142 to obtain the voltage pulsation degree ΔE ₀ ′ / E ₀ . . Further, the output of the dividing means 143 is multiplied by the output f ₀ of the adding / subtracting means 9 by the multiplying means 144 to output an inverter frequency adjustment Δf ₀ (= ΔE ₀ 'f ₀ / E ₀ ).

Now, the correction coefficient K given to the multiplying means 17
_{If C} is assumed to be 1, and Δf ₀ ′ = Δf ₀ , the inverter operation frequency command f ₀ is corrected by the adjustment Δf ₀ .

That is, the adjustment Δf ₀ is added to the addition / subtraction means 9.
Is added to the output f ₀ by the adding means 15 to obtain an inverter frequency command f (= f ₀ + Δf ₀ ).

Here, assuming that the pulsation rate of the inverter input voltage E is K and the pulsation ΔE ₀ pulsates in a sinusoidal manner with the frequency f _e , the inverter input voltage E and the frequency command f are expressed by the following equations. Is represented.

[0020]

E = E ₀ + ΔE ₀ = E ₀ + KE ₀ sin (2πf _e t) (Equation 1)

[0021]

[Number 2] _{f = f 0 + Δf 0 =} f 0 + ΔE 0 'f 0 / E 0 = f 0 + Kf 0 sin (2πf e t + α) ... ( number 2) where, α: ripple component actual value ΔE ₀ and detection The phase difference between the values ΔE ₀ ′.

When the output frequency command f of the inverter 4 in the equation (2) is given to the PWM modulating means 7, the modulated wave generating means 72 modulates the U, V, and W phase modulated wave signals G represented by the following equations. _U, G _V, and outputs the G _W.

[0023]

(Equation 3)

[0024]

(Equation 4)

The relationship between the input voltage E of the inverter 4, the adjustment Δf ₀ of the inverter frequency, and the outputs (G _U , G _V ) of the modulated wave generating means 72 is as shown in FIG. 5, for example. Here, the pulsation ΔE ₀ of the input voltage E of the inverter 4
Frequency f _e = output f ₀ of addition / subtraction means 9, pulsation ΔE ₀
And the detected value ΔE ₀ ′ (| ΔE ₀ ′ | = | ΔE ₀ |) has a phase difference α = 0. The output of the modulated wave generation means 72 is
The second term of equation (4), that is, the adjustment amount Δ of the inverter frequency
f ₀ changes from the dotted line to the solid line in FIG. As a result, when the output voltage of the inverter 4 is pulse number = 1 pulse (modulation rate γ = sine wave peak value / triangular wave peak value ≧ 1 in FIG. 2A), the CVVF control region in FIG. From the dotted line of 5 (D) to the solid line, the imbalance between the positive and negative half cycles is significantly reduced.

Here, the amount of imbalance in the positive and negative cycles of the output voltage of the inverter 4 will be described mathematically with reference to FIG.

In FIG. 5C, the modulated wave generating means 72
Are the dotted lines G _U ′ and G _V ′, G _U ′ and G _V ′ are 0.
T _U ′ and T _V ′ are

[0028]

(Equation 5)

[0029] a is also G _U output by the solid line of the modulation wave generation means 72, at the G _V, G _U and G _V is 0 T _U and T
_V is

[0030]

(Equation 6)

## EQU1 ## ΔT _U and ΔT _{V in} equation (6)
Is given by Equations (3) to (6),

[0032]

(Equation 7)

## EQU1 ##

(1) When Beatless Control According to the Present Invention is Not Performed When the output frequency adjustment Δf ₀ of the inverter 4 does not exist,
That is, the voltage-time product ET 'of a half cycle of the output voltage of the inverter 4 indicated by the dotted line in FIG. 5D corresponding to the modulated waves G _U ' and G _V 'indicated by the dotted line in FIG. Definitely integrates

[0035]

(Equation 8)

Here,

[0037]

(Equation 9)

## EQU4 ## From the equations (8) and (9), the imbalance ΔET ′ (= (ET ′ (N) −ET ′) between the positive and negative half cycles of the output voltage of the inverter 4 is obtained.
(N + 1)) / 2) has a magnitude | where the output f _{0 of the} frequency command is near the pulsation frequency f _e of the inverter input voltage.
K ′ |, and fluctuates (ie, beats) at the frequency (f ₀ −f _e ). Even if the magnitude | K '| is smaller than the first term (E ₀ / 3f ₀ ) of the equation (8), its frequency (f ₀
Where −f _e ) is small, the impedance of the induction motor 5 becomes small, so that an excessive current flows through the induction motor 5, which causes commutation failure or breakage of the inverter 4, and the torque of the induction motor 5 also pulsates greatly. Will do.

(2) In the case of beatless control according to the present invention When the output frequency adjusting means 14 of the inverter 4 is provided, that is, FIG. 5 (D) corresponding to the modulated waves G _U and G _V indicated by the solid lines in FIG. The voltage-time product ET of a half cycle of the output voltage of the inverter 4 indicated by the solid line in FIG.

[0040]

(Equation 10)

## EQU1 ## This equation (10) is obtained by calculating the pulsation ΔE ₀ of the input voltage E of the inverter 4 and the adjustment Δ
Assuming that the phase difference α of f ₀ is 0, the second term and the third term cancel each other and become (E ₀ / 3f ₀ ). That is, the imbalance amount (= (ET (N) −ET (N + 1)) / 2) between the positive and negative cycles of the output voltage of the inverter 4 becomes 0, and the beat phenomenon of the output voltage of the inverter 4 is suppressed.

By the way, particularly in the railway train, to increase the breakdown voltage utilization of the GTO thyristor to be used in the inverter, as shown in FIG. 3, at a frequency corresponding to approximately half the speed n ₀₁ of the rated speed n ₀ of the train It saturates the inverter to the maximum voltage and at higher speeds only adjusts the frequency. Thus, as shown, about half of the speed n ₀₁ above the rated speed n ₀ of the train, the adjustment of the inverter output voltage becomes 1 pulse uncontrollable. On the other hand, the inverter frequency is continuously changed over the entire speed range.

Therefore, the AC power supply 1 shown in FIG.
Then, the frequency f _e of the rectifying ripple of the converter 2 is 100 Hz, and in the speed range where the inverter frequency passes this frequency, the inverter 4 has already entered the one-pulse control (CVVF control region in FIG. 3).

In such a case, according to the above-described principle, the beat phenomenon which is generated when the inverter frequency f approaches the rectified ripple frequency f _e of the converter 2 is effectively suppressed, and the smooth speed of the inverter train is obtained. Realize control.

Next, in order to confirm the effectiveness of the above-described method, the capacity of the induction motor 5 is set to 130 KW (rated: voltage 1).
100 V, current 86.7 A, frequency 75 Hz), the slip frequency command fs is fixed (3 Hz), and the input voltage E of the inverter 4 is expressed by the following equation (DC component E ₀ = 1500).
V, pulsation rate K = 6%, frequency f _e of pulsation component ΔE ₀ = 10
0 Hz), and the result of digital simulation performed by a large computer will be described below.

FIG. 6 shows that the reference command f ₀ of the inverter frequency is 103 Hz (the rotation frequency f _n of the induction motor 5 = 100H).
It is a simulation result in the case of z). FIG.
(A) is a case where there is no adjustment amount Δf ₀ of the inverter frequency. As a result, as described above, due to the imbalance between the positive and negative cycles of the output voltage of the inverter 4, the current of the induction motor 5 greatly beats at the frequency (f ₀ −f _e ) = 3 Hz, and the torque of the induction motor 5 It can also be seen that the pulsation of the input voltage E of the inverter 4 also greatly pulsates at the frequency f _e (= 100 Hz) of the pulsation ΔE ₀ . FIG. 6B shows a case where the output frequency command f of the inverter 4 is adjusted by the output Δf ₀ of the output frequency adjusting means 14 of the inverter 4 by setting α = 0 in the equation (2), as described above. .

From this, it can be seen that the beat phenomenon of the current of the induction motor 5 is almost eliminated, and that the torque of the induction motor has a slight pulsation, but much smaller than that of FIG. FIG. 6C shows a case where α = −5 ° by variously changing α in Expression 2 in order to further reduce the torque pulsation of the induction motor 5.

Thus, the current of the induction motor 5 is
It can be seen that there is almost no difference from (B), and the torque pulsation of the induction motor 5 is almost eliminated. That is,
From the point of torque pulsation of the induction motor 5, α
It turns out that it is only necessary to set properly.

Therefore, symbols relating to the current and torque of the induction motor 5 are defined as shown in FIG. 7, that is, the peak current of the induction motor 5 when the input voltage E of the inverter 4 has no pulsation ΔE ₀ is i _Pn , Average value is T _av (Fig. 7
(A)). Further, the increase in the peak current of the induction motor 5 due to the pulsation ΔE ₀ of the input voltage E of the inverter 4 is Δi _PW (= i _PW −i _Pn ), and the pulsation of the torque is ΔT _b (FIG.
As (B)), FIGS. 8 and 9 show simulation results of Δi _Pb (i _Pn ) and ΔT _b (T _av ) when the reference command f ₀ of the inverter frequency is variously changed.

8 and 9, it can be seen that the peak current increase Δi _{Pb of} the induction motor 5 (FIG. 8) and the torque pulsation ΔT _b
(FIG. 9) shows a case where there is no inverter frequency adjustment Δf _{0, as} indicated by a two-dot chain line, the inverter frequency reference command f
₀ ≒ Pulse frequency f _e of inverter input voltage (= 100H
It can be seen that it becomes the largest at z). This Δi _Pb
And ΔT _b can be significantly increased as indicated by the dashed line (FIGS. 8 and 9) when the inverter frequency command f is adjusted by the inverter frequency adjustment amount Δf ₀ by setting α = 0 ° in the equation (2) as described above. Become smaller. However, f ₀ and f _e (= 100H
Where the difference between the z) is large, compared to the place of f ₀ ≒ f _e, it was found to be somewhat larger.

To improve this, the frequency adjustment amount correction means 16 is provided, and its output (correction coefficient) K _C is multiplied. That is, the inverter frequency command f is

[0052]

[Number 11] so as to adjust as _{f = f 0 + Δf '=} f 0 + K C Δf 01 = f 0 + K C Kf 0 sin (2πf e t + α) ... ( number 11), with α = 0, K _C Were varied and simulations were performed.

As a result, K _C is equal to the inverter input voltage E
Ripple component divided by the division means 161 at a rotational frequency f _n of the induction motor 5 the frequency f _e of the Delta] E _0, multiplying means its output
162 squared, ie

[0054]

Equation 12] K _C = if ^{_{(f e / f n) 2}} ... ( Equation 12), ripple component [Delta] T _b of the increase .DELTA.i _Pb and peak torque current of the induction motor 5, 8 and 9 It was found to be improved as indicated by the dotted line.

As described with reference to FIG. 6, in order to further improve the torque pulsation ΔT _b , the equation (11) and the equation (1)
In the equation 2), when α is changed as shown in FIG. 9 with respect to the reference command f ₀ of the inverter frequency, ΔT _b hardly occurs as shown by the solid line in FIG.

At this time, the increase Δi _Pb of the peak current of the induction motor 5 does not change much as shown by the solid line in FIG.

The above simulation result is a case where the number of pulses of the output voltage of the inverter 4 is one pulse (see FIG. 5), that is, the output (modulation rate) γ of the voltage control means 13 is one. A similar result (effect) can be obtained even in the case of multiple pulses (γ <1). In this case, the correction coefficient K _C for correcting the adjustment amount Δf ₀ of the inverter frequency is:

[0058]

(Equation 13)

It has been confirmed by simulation that the output of the multiplying means 162 is more effectively divided by the modulation factor γ. When starting the induction motor 5 and at a low speed, as can be seen from the equations (12) and (13), K _C becomes too large, so it is advisable to limit K _C.

Finally, FIG. 10 shows a specific example of the detecting means 142 for detecting the DC component E ₀ of the input voltage E of the inverter 4 and the detecting means 141 for detecting the pulsation ΔE ₀ .

[0061] That is, the detection unit 142 of the DC component E ₀ of the input voltage E of the inverter 4 is a smoothing circuit consisting of an operational amplifier OP2 resistor R _e 21, R _e 22 and R _e 23 and the capacitor C2, the gain ( = _Re 23 / _Re 21)
Is set to 1 and the time constant (= _Re 23 × C2) is set to be large. The detection means 141 of the ripple component Delta] E ₀ of the input voltage E of the inverter 4, the resistor R _e. 11 to an operational amplifier OP1
R _e 15 and the capacitor C11, a bandpass circuit consisting of C12. The gain and phase characteristics of this circuit are
As shown in FIG. 11, the gain is 1 (input ΔE _{0) at} the frequency f _e of the pulsating component ΔE ₀ of the input voltage E of the inverter 4.
_{0 (} the magnitude of the output ΔE ₀ ′) and the input phase, that is, the phase difference α between the pulsation component ΔE ₀ and the frequency adjustment amount Δf ₀ is:
As described in FIG. 9, so that the appropriate value for the inverter frequency reference command f _0, switched by the switch S1~S3 in accordance with the magnitude of the reference command f _0.

As described above, according to the embodiment of FIG. 1, the output voltage of the inverter 4 and the output voltage of the induction motor 5 caused by the pulsation ΔE ₀ (rectifying ripple of the converter 2) included in the input voltage E of the inverter 4 Since the beat phenomenon of the current can be suppressed, an excessive current does not flow through the induction motor 5, the commutation failure or breakage of the inverter 4 can be prevented, and the torque pulsation of the induction motor 5 is suppressed, so that the induction motor 5 can be smoothly operated. There is an effect that can be driven.

Although the embodiment of FIG. 1 has been described with reference to the case where the number of pulses of the output voltage of the inverter 4 is one (see FIG. 5), the above-described effects can be obtained even when the number of pulses is large. Of course is not compromised.

[0064]

According to the present invention, the beat phenomenon of the output voltage of the inverter and the current of the induction motor caused by the pulsation component (rectifying ripple of the converter) included in the input voltage of the inverter can be effectively suppressed. There is an effect that excessive current does not flow through the motor, commutation failure and damage of the inverter can be prevented, and the load can be operated smoothly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a control device for an induction motor using a converter / inverter according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation of pulse width modulation based on comparison of a sine wave triangular wave.

FIG. 3 is a diagram showing a relationship between a pulse number and an inverter output voltage with respect to a reference command for an inverter output frequency.

FIG. 4 is a diagram showing a waveform relationship between an input voltage and an output voltage of an inverter.

FIG. 5 is an explanatory diagram of suppression of a beat phenomenon of an inverter output voltage.

FIG. 6 is a simulation waveform diagram of current and torque of an induction motor.

FIG. 7 is a definition diagram of symbols relating to current and torque of an induction motor.

FIG. 8 is a simulation result regarding a peak current of the induction motor.

FIG. 9 is a simulation result regarding torque pulsation of an induction motor.

FIG. 10 is a specific example of a means for detecting a direct current component and a pulsating component of the inverter input voltage.

FIG. 11 is a gain and phase characteristic diagram of a means for detecting a pulsating component of the inverter input voltage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply, 3 ... Filter capacitor, 4 ... Pulse width modulation inverter, 7 ... Modulation means, 9 ... Addition / subtraction means, 14
... inverter output frequency adjusting means, 15 ... adding means,
16. Means for correcting the amount of adjustment of the inverter output frequency, 1
7, 144, 162 multiplication means, 143, 161, 163
... Division means.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshio Tsutsui 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. Inside the factory (72) Inventor Katsuaki Suzuki 4-6 Kanda Surugadai, Chiyoda-ku, Tokyo Inside Hitachi, Ltd.

Claims (2)

[Claims] 1. A converter for converting AC to DC, a smoothing capacitor for smoothing DC rectified by the converter, an inverter for converting the smoothed DC to three-phase AC, and an output voltage of at least the inverter. In a power converter including constant voltage variable frequency (CVVF) control means for variably controlling the frequency of a voltage pulse having one pulse included in a half cycle of an output voltage of the inverter in a region where the inverter cannot be controlled in a maximum range, Means for detecting a pulsation caused by the rectification of the converter included in the DC input voltage, and in response to the pulsation, when the pulsation increases the DC input voltage of the inverter, narrows the pulse width of the output voltage of the inverter. When the DC input voltage of the inverter decreases due to the pulsation, Means for increasing the pulse width of the pressure. 2. A converter for converting AC to DC, a smoothing capacitor for smoothing DC rectified by the converter, an inverter for converting the smoothed DC to three-phase AC, and an output voltage of at least the inverter. In a power converter including constant voltage variable frequency (CVVF) control means for variably controlling the frequency of a voltage pulse having one pulse included in a half cycle of an output voltage of the inverter in a region where the inverter cannot be controlled in a maximum range, Means for detecting the degree of pulsation caused by rectification of the converter with respect to the DC input voltage, and, according to the degree of pulsation, the pulse width of the output voltage of the inverter when the DC input voltage of the inverter increases due to the pulsation. The inverter when the pulsation reduces the DC input voltage of the inverter. Means for adjusting to increase the pulse width of the output voltage of the power converter.