JPH02206385A - Current type inverter - Google Patents

Abstract

PURPOSE:To increase output voltage from an inverter section by arranging a means for varying duty factor at the inverter section. CONSTITUTION:A converter section 1 for converting AC power into DC power, a DC reactor 2 for smoothing the ripple of output current from the converter section 1, an inverter section 3 for converting DC power into variable voltage variable frequency power, an induction motor 4 to be driven through the inverter section 3, and the like are arranged. In particular, means for varying the duty factor lambdai is arranged at the inverter section 3. The duty factor lambdai is the ratio between DC current at the input of the inverter section being fed from the converter section 1 to the inverter section 3 and output current at the inverter section being fed to the induction motor 4. By such arrangement, a current type inverter for increasing the output voltage from the inverter section 3 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current source inverter, and more particularly to control of the conduction rate of an inverter section that supplies alternating current power to an induction motor.

[Conventional technology]

Conventional current source inverters are described in the technical magazine "Hitachi Hyoron Vo.
1. 68 & 6 (1986-6) Jl no P, 49
5~P, 500'"Sinusoidal inverter controlled high speed elevator", the principle configuration is explained in FIG. 3 of the publication, and an example of application in a high speed elevator is explained in FIG. 9. .

[Problem to be solved by the invention]

Figure 6 shows the basic configuration of a current source inverter, where 1 is a converter section, 2 is a DC reactor, 3 is an inverter section,
4 is induction fi! There are 111 aircraft. The PWM control unit and vector control unit are omitted.

When such a current source inverter is driving an induction motor as a load, a linear relational expression approximately holds true.

3JwoVd"F X VacXcos'p Xλc
−=(1)π In addition, Vac: AC power supply voltage Iac of the converter section? AC power supply current λC of the converter section: Conductivity T of the converter section: Control phase angle Vd of the converter section: Input side DC voltage of the inverter section d: Input side DC current of the inverter section vo: Output voltage of the inverter section ■o : Output of the inverter section 'forward current 0: Control phase angle of the inverter section In equation (1), cos ψ is l in all regions except the near-zero region of the DC voltage vd. ). That is, the DC voltage vd has a current conductivity λ of the converter section over almost the entire region.

The DC voltage Va is controlled by changing only the voltage Va. Therefore, for simplicity, this conductivity λC is set to 0≦λc<1
Then, equation (1) can be approximated by equation (5).

G,”,V++ valve XVacXλcXsigh[co
Considering the case where s'P]-(s)π cos 'f'≧O (during power running), (5)
The formula is G Vd4 X Vac Xλc −(
6) π becomes.

Therefore, the output voltage Vo of the inverter section is (2), (6
), COSθ is obtained. Here, the control phase angle cosθ of the inverter section is
Since the induction motor is vector controlled, it matches the power factor of the induction motor.

Now, consider the maximum output voltage of the inverter section.

From equation (7), when λc:1, the output voltage Vo is twice the maximum. In general, the maximum power factor of an induction motor is about 0.85, so the output voltage Vo can be at least an AC power source.

On the other hand, when considering the power supply voltage Vae, 20
% may decrease. That is, if the rated value of the power supply voltage is Vao, then Vac = VaoX 0, 8 ・
...It is necessary to consider up to (8).

Therefore, the maximum output voltage that the inverter section can supply at this time is under the worst condition (=when the power factor of the induction motor is at its maximum) (assuming the maximum power factor is 0.85). That is, at this time, the inverter section can only supply voltage up to 94% of the rated power supply voltage value.

From the above, the rated voltage of the induction motor, which is the load of the inverter section, must be set at least 10% lower than the rated value of the power supply voltage, taking into consideration the voltage margin. For example, if the rated value of the power supply voltage is 400V, an induction motor with a rated voltage of 360V or less will be selected. If this problem can be solved, the rated voltage of the induction motor can be set to be equal to or higher than the power supply voltage, in the above example, 400 V or higher.

If the rated voltage of an induction motor can be changed from 360V to 400V, the rated current will decrease by about 10%, so the load current will also decrease by the same amount. =0.81 or about 20
% can be reduced.

In other words, conventional current source inverters can
It can be said that this output voltage cannot be lowered due to various factors.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a current inverter in which the output of the inverter section can be increased.

Another object of the present invention is to provide a current source inverter that can increase the output voltage of the inverter section by adjusting the current conduction rate of the inverter section.

Another object of the present invention is to provide a current source inverter that can obtain an output voltage from the inverter section as if there had been no voltage drop even if the AC power supply voltage of the converter section decreases.

Still another object of the present invention is to provide a current source inverter that can reduce copper loss in an induction motor, a DC reactor, etc. when the AC power supply voltage of the converter section decreases.

[Means to solve the problem]

In order to achieve the above object, in the present invention, means for making the conduction rate variable is provided in the inverter section.

The current flow rate referred to here is the ratio of the inverter inlet DC current supplied from the converter to the inverter and the inverter output current supplied to the induction motor, as has been conventionally used. be.

[Effect]

By introducing the same concept of conduction rate as on the converter side to the inverter side, equations (2) and (4) can be expressed as the following equations.

Here, λN=conductivity of the inverter section (0×λ1≦1) Therefore, equation (7) becomes the following equation.

If we make λ equal to the coefficient, that is, λ always becomes λs=k
...If the settings are made as shown in (15), then the output voltage vO is determined by the equation (14), and the equation (12) is the current conductivity λ of the inverter section,
This shows that the output voltage Vo of the inverter section can be increased by decreasing .

Furthermore, it shows that the output voltage vO can be increased more than the AC power supply voltage Vac with a power factor of CO8θ.

Now, the AC power supply voltage Vac of the converter section is V ac = k X V ao with respect to the rated value Vao of the power supply voltage.
・= (13) k: power supply reduction coefficient (0<k≦1), then equation (12) becomes the following equation.

Here, the conduction rate λ1 of the inverter section is reduced as the power supply decreases,
It is no longer affected by a drop in the AC power supply voltage Vac.

However, if the conduction rate of the inverter section is changed, the output current Io will also vary, as can be seen from equation (11). Therefore, when changing the conduction rate λ1, it is preferable to set the command value of the DC current Ia to 1a"IaoX λ5"IdoX- (17) Iao: true command value of the DC current. As a result, equation (11) becomes (14), (
17) From the formula, Ia.

IO=□...(18
)JΣ, and the output current Io of the inverter section is no longer influenced by the conduction rate λ1.

Therefore, in the conventional current source inverter, equation (14) and (17)
) It is possible to maintain the output voltage and output current regardless of a drop in the power supply voltage by simply adding a function that satisfies the relational expression shown in the following equation. Here, equation (14) narrows down the current conductivity of the inverter according to the decrease in the electric current rX voltage, and (
Equation 17) means that the DC current is increased in inverse proportion to the decrease in the power supply voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is a converter section that converts alternating current into direct current, 2 is a direct current reactor that smoothes the output current ripple of converter section 1, and 3 is an inverter section that converts direct current into variable voltage and variable frequency.

4 is an induction motor driven by an inverter section 3, and a rotary encoder R for speed feedback is attached to the shaft end. 14 is a speed control device that calculates an output of 1 herk based on the deviation between the speed command ω and the umbrella and the speed feedback ω; 15 is the speed control device 14
The I-lux command and speed feedback ω output from
This is a vector control device that calculates three elements for the output current of the inverter section 3, namely, a current command (2), a phase command (r), and a frequency command (ω). 10 is a current limiter circuit that limits the output current, and 9 is a current control circuit that calculates a DC voltage command Vdn from the deviation between the actual current command 16* and the feedback value 1d of the DC current detected by the Hall CT 5. 8, 11, and 13 are nonlinear elements that determine the conduction rate λC1 of the converter section 1, the increment α in the DC current, and the conduction rate λC1 of the inverter section 3 from the DC voltage command Vd, respectively.

Reference numeral 6 denotes a transformer for power synchronization of the converter section], and 7 is a PWM control circuit for the converter section which generates actual pulses from the power supply synchronization signal and the conduction rate λC of the converter section 1. 12 is a PWM control circuit for the inverter section which does not generate a pulse actually applied to the inverter section 3 from the phase command *, the frequency command ω*1 and the conduction rate λ1. Note that PWM stands for pulse width modulation.

Next, I will explain the operation′! J1. To make it easier to understand, we will first explain the definition of conductivity using the converter side as an example.

FIGS. 2(a) and 2(b) show the main circuit configurations of the converter section 1 and the inverter section 3, respectively, in which reference numerals 21 and 31 are transistor modules, and 22 and 32 are filter capacitors.

Since the transistor used as a self-extinguishing element in the main circuit does not have a reverse voltage blocking function, a diode is connected in series, but this diode can be omitted if a gate turn-off thyristor having a reverse voltage blocking function is used.

Figures 3 and 4 show the current Iu flowing through each part of Figure 2(a).
This shows the relationship between Iau and d using actual waveforms (
Iac in Figure 1 is expressed as Iau as U phase)
. As a special example, FIG. 3 shows waveforms in the case where the conductivity is 1, with (a) showing the waveform when the direct current Id is large and (b) showing the waveform when the direct current Id is small. The rectangular wave current A is smoothed by the filter capacitor 22 in FIG. 2, and becomes a sinusoidal current as indicated by the broken line Iau. Here, in order to make Iau a sine wave, if the carrier period is T, the pulse width Δt at an arbitrary angle γ point may be determined as Δt=T-5inγ (19). On the other hand, the converter section 1 needs a function that can vary the DC output voltage, and this is performed not only by phase control but also by pulse width control. That is, by uniformly multiplying the pulse widths of all the pulses shown in FIG. 3 by a proportionality constant λ, the DC output voltage is varied while satisfying the input current as a sine wave. Specifically, the pulse width Δt at an arbitrary angle γ point is Δt=λ・T−sin y −(20)
At this time, the following relational expression holds true between the power supply voltage Vac and the DC output voltage Vac of the converter section 1.

π Here, (P: control phase angle) Also, the following relational expression holds true between the input current Iau (effective value) and the DC output current.

V'rX I a poem■6・λ...(22)
J7×Eng.

,”-Ia gradient...(2
3) λ (20) The proportionality constant λ in equations (23) is defined as the conduction rate.

The operation shown in FIG. 1 will be explained below.

First, rotary encoders R and E control the induction motor 4.
By detecting the shaft speed ω, and inputting the deviation between this and the shaft speed command value ω, into the ASR 14, the torque command τ
A skewer is generated. By inputting this τ umbrella and shaft speed ω to the vector control device 15, three elements for the inverter output current, namely, current command I-1, phase command θ, and frequency command ω* are output. Here, the current command 1 is sent to the converter section, and the phase command .theta.1 and the frequency command .omega. are sent to the inverter section.

The current command ■* to the converter section is obtained by adding the output of the nonlinear element 11 newly added in the present invention, that is, the product (αI*) with the DC current increase coefficient α, to obtain the actual DC current command Ia* (
Id*=I*+αI*) and is input to the current control system via the current limiter 10. This value I4* and Hall CT
The deviation from the current feedback signal from 5 is determined by the current control circuit (ACR).
)9. ACR9 calculates and outputs a DC voltage command v*. DC voltage command v by nonlinear element 8
, the conductivity λC suitable for the tree is determined, and the PWM control circuit 7
The converter section 1 is moved by this. Actually, not only the conduction rate λ6 but also the phase command is input to the PWM control circuit 7, but since the phase command region is narrow and to simplify the explanation, it is omitted as cos'p = 1 (fixed).

Also, the conductivity rate λ. cannot actually be ambience or 1, but for the sake of simplicity, it will be explained as O≦λC≦1−. Therefore, the relationship between the output voltage Vac of the converter section 1 and λC at this time is expressed by the following equation from equation (21).

π Consider now the decrease in AC power supply voltage Vac. Even if the AC power supply voltage Vac decreases, the DC output voltage V of the converter section 1
In order to keep ac constant, the conduction rate λ must be increased accordingly. needs to be made larger. This itself is automatically adjusted by increasing the DC voltage command ■4 in the ACR system, but the conduction rate λ. Since there is a hardware constraint of O≦λ≦1, the conduction rate λC will be saturated if the AC power supply voltage Vac decreases significantly. Here, if the value of the DC voltage command ■d* when λc"1 is set to Va"max, the shortage of the power supply voltage Δv6 is ΔV@=Va main - vd min,,, -(25
) (holds when V, *≧V, and maX).

On the other hand, considering the inverter section 3, the vector control device 15
By inputting 0 and W outputs from the inverter section 3 to the PWM control circuit 12, the inverter section 3 shapes the DC current Ii into a waveform. At this time, the DC current Vd, the output voltage Vo, the DC current, and the output current I. The relationship with
6) π 1d=&XIo (27). This corresponds to when the conduction rate λ is set to λ=1 in equations (21) and (23). Here, in the present invention, the inverter section is also configured to vary the conduction rate λi similarly to the converter section. That is, providing the nonlinear element 13,
The PWM of the inverter unit 3 is determined so that the conduction rate λt can be determined by determining the conduction rate λt from the DC voltage command v, *.
Added the function of control circuit 12. By doing this, equations (27), (28), %, and % (29) are obtained. This is transformed into VdXCO5O*Xλ1.

Now, if the power supply voltage has decreased beyond a predetermined value, as mentioned above, the conditional expression V in equation (25): You can find it by . Now, assuming the voltage shortage rate Q, the output voltage Vo at this time is π Here, Vao is the DC side voltage supplied when the power supply is normal. Therefore, in order to make the output voltage Vo a normal value, λ8 in equation (34) is set to λ, and white 1 is set to ΔV.

This can be achieved by correcting Vd"max vdmin1taX (however, v1 ≧ V, umbrella, &8 o'clock holds). At this time, equation (34) becomes π, and the output voltage Vo is no longer influenced by the power supply voltage.

If formula (35) is graphed, it becomes nonlinear element 13.

Here, the relationship between the output current 0 and the λ eclipse is expressed by equation (32), so if the DC current Id is constant, the λ eclipse also decreases as the λ eclipse changes. To compensate for this, the DC current I4 is changed to the original command value * = (1 + α) 1 min... (37) ■, Umbrella - Va min max (holds true when Vd rate ≧ Vd * max) It is necessary to do so. If formula (37) is graphed, it becomes nonlinear. FIG. 5 shows detailed characteristics of these nonlinear elements.

Each characteristic in FIG. 5 shows the current conduction rate of the inverter unit 3 when the DC voltage command Val cannot make the output voltage Vo of the inverter unit 3 a desired value depending on the conduction rate λC of the converter unit 1. This shows that λ1 is lowered and the DC current command 11 is increased. 1 Normally, as in the past, the conduction rate of the inverter section 3 is maintained at a value close to the maximum, for example 0.95, and the inactive portion of the inverter section 3 (directly returned from the inverter section 3 to the converter section 1) is , the current that does not flow to the induction motor 4 side) is kept as small as possible, while taking care not to generate high voltage in the DC reactor 2, and only when the power supply voltage has significantly decreased, the current flow rate of the inverter section 3 is used to This is to prevent the voltage applied to the motor 4 from changing.

As described above, according to this embodiment, the output voltage of the inverter can be stably supplied without being affected by a drop in the power supply voltage, so there is no need to consider voltage coordination with the induction motor when the power supply voltage drops. The rated voltage can be set higher.

Therefore, the rated current of the induction motor decreases, and the load current also decreases, so that copper loss in various parts such as the induction motor and the DC reactor can be dramatically reduced.

However, although it is possible to increase the output voltage of the inverter by making the current flow rate of the inverter section smaller than the steady state, the DC side current also increases, so if the rated voltage of the induction motor is increased unnecessarily, the copper Not only the loss increases, but also the main circuit element capacitance increases.

However, in a situation where there is no need to consider the increase in reactive components in the inverter section, the conduction rate λC of the converter section 1 is saturated (
Even if λc=1), the conduction rate λ1 of the inverter section 3 may be lowered and the output voltage Vo of the inverter section 3 may be increased.

If the power supply voltage and the rated voltage of the induction motor are the same, there is no need to change the current flow rate of the inverter under most power supply conditions, and therefore the load current will decrease by the amount that the rated current of the motor has decreased. can be reduced by about 20%.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a current source inverter that can increase the output voltage of the inverter section by changing the conduction rate of the inverter section.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram showing one embodiment of the present invention;
Figures (a) and (b) are main circuit configuration diagrams of the converter section and inverter section, Figures 3 (a) and (b) are waveform examples showing the relationship between PWM pulses and output current, and Figure 4 is the output current and Examples of waveforms showing the relationship between the return current rate and FIGS. 5(a) to (c) output the converter measurement current rate λC, the inverter side conductivity rate λ, and the DC current increase coefficient α from the DC voltage command Vt tree. FIG. 1 is a characteristic diagram of the nonlinear elements shown in FIG. 1, and FIG. 6 is a diagram showing the principle configuration of a current source inverter. 1...Converter section, 2...DC reactor, 3.
...Inverter section, 4...Induction motor, 14...A
SR115...Vector control circuit, 9...ACR1
8... Nonlinear element that sets the conductivity λC on the converter side, 11... Nonlinear element that sets the increase in DC current, 13... Nonlinear element that sets the conductivity λ1 on the pine converter side. fig fig fig fig fig fig fig fig fig fig fig fig fig fig fig fig.

Claims (1)

[Scope of Claims] 1. A converter section that converts alternating current into direct current and controls the direct current, a direct current reactor that smoothes the direct current of the converter section, and a variable voltage variable frequency alternating current power connected to the direct current reactor. A current source inverter that includes an inverter section that converts AC power into AC power, and drives an induction motor connected to the inverter section using the AC power, the inverter section being equipped with means for making the conduction rate variable. inverter. 2. In a current source inverter that includes a converter section and an inverter section in which PWM control and vector control are performed, and drives an induction motor with AC output from the inverter section,
A current source inverter characterized in that the inverter section is equipped with means for varying the current conduction rate. 3. The current source inverter according to claim 1 or 2, wherein the inverter section uses a self-extinguishing element as a main circuit control element. 4. The current source inverter according to claim 1 or 2, wherein the conduction rate variable means lowers the conduction rate when the voltage applied to the induction motor decreases. 5. In the above claims 1 and 2, when the voltage applied to the induction motor is a predetermined value, the conduction rate variable means sets the conduction rate to a rated value near the maximum value, and A current source inverter characterized in that the conduction rate is reduced when the voltage applied to the inverter falls below a predetermined value. 6. A converter section that converts alternating current into direct current and controls the direct current, a direct current reactor that smoothes the direct current of the converter section, and an inverter section that is connected to the direct current reactor and converts direct current into alternating current power with variable voltage and variable frequency. In a current source inverter that drives an induction motor connected to an inverter section with said AC power, means for varying the conduction rate of the inverter section, controlling the DC current in inverse proportion to said conduction rate. A current source inverter comprising: 7. In the above claim 6, the conduction rate variable means lowers the conduction rate when the voltage applied to the induction motor decreases, and the DC current control means increases the DC current when the conduction rate decreases. A current source inverter characterized by: 8. In claim 7, the conduction rate variable means sets the conduction rate to a rated value near the maximum value when the voltage applied to the induction motor is a predetermined value; A current source inverter characterized in that the current source inverter reduces the conduction rate when the current flow rate falls below a predetermined value. 9. In the above claims 1 and 2, the conduction rate variable means has a characteristic of lowering the conduction rate of the inverter section in a situation where the conduction rate of the converter section is saturated. A current source inverter featuring: 10. The current type according to claims 1 and 2, characterized in that the conduction rate variable means provides a conduction rate equal to the ratio of the actual input voltage to the rated voltage of the converter section. inverter. 11. In the above claims 1 and 2, when the conduction rate variable means provides a conductivity that is significantly greater than the ratio between the actual input voltage of the converter section and the rated voltage, the converter section is adjusted by the reciprocal of the ratio. A current source inverter, characterized in that it is provided with direct current control means for increasing the direct current flowing from the source to the inverter section.