JPS6154896A - Power converter - Google Patents

Abstract

PURPOSE:To continue to stably operate an AC motor when a PWM control and a PAM control are switched by adding the first correcting means for instructing acceleration or deceleration, and the second correcting means for compensating the variation in the phase of the voltage. CONSTITUTION:A power converter has an acceleration/deceleration instructing circuit 41 for generating a correction signal ec for instructing an acceleration/ deceleration speed upon receiving of PWM control, PAM control signals eb1, eb2, and an adder 42 for adding a correction signal ec as a reference ea. Since the signals eb1, eb2 are received to stepwisely vary the voltage phase, a phase correcting circuit 43 for generating a correction signal ed of frequency increase or decrease in a short period, and an adder 44 for adding the signal ed only to the frequency reference to obtain a new frequency reference signal ee are provided. Thus, an AC motor of a load even at both control switching time can be stably continued to operate.

Description

[Detailed Description of the Invention] [Technical Field of the Invention 1] The present invention relates to a power conversion device for driving an alternating current electric current, and in particular, a power conversion device for driving an alternating current electric current. It has both control means of a valve (a method of controlling the frequency with an inverter circuit and the voltage with a DC voltage, hereinafter referred to as PAM control), and even when these control means are switched and used, the AC motor can be stabilized. The present invention relates to a power conversion device that can continue to be driven.

[Technical background of the invention and its problems] Various main circuit systems have been put into practical use in power conversion iA devices that drive AC power supplies, but low-order harmonic components or specific P to remove harmonic components of
WMI! Voltage source inverters are often used because it is easy to adopt i-control. In addition to the above advantages, if PWM control is adopted, the voltage and frequency of the output AC can be arbitrarily controlled, so the advantage is that the control coordination is excellent and the power factor on the power source side can be improved. Therefore, it is desirable to use it over as wide a frequency range as possible. However, at high output frequencies PWM
Performing control requires a correspondingly high switching frequency from the main switching elements constituting the inverter circuit, which is disadvantageous in terms of device efficiency in the case of a silis inverter or a human-harm ff1GTo inverter.

Therefore, the output AC voltage is controlled by PWM control in the low frequency region and DC voltage control in the high frequency region, and the inverter circuit controls only the frequency of the output AC.
By switching and using itII'n, an ideal power conversion device can be constructed.

FIG. 9 shows a block diagram of a voltage source inverter using PWM control and PAM control/deduction switching type.

The main circuit obtains smoothed direct current through a rectifier circuit 12, a direct current reactor 13, and a smoothing capacitor 14 connected to the alternating current voltage a11, and can be regarded as a direct current power source as a whole. The inverter circuit 15 converts direct current into alternating current to drive an alternating current electric motor (hereinafter referred to as an induction motor). As for the control circuit, a speed reference is given by a setter 21, and via an input limiting circuit 22 becomes a slowly changing voltage/frequency reference 2a. The reference ea is compared with the frequency fa set by the setter 23 in the comparator 24, and the PWM control signal eb1 is set below the frequency 0, the PAM control signal e is set below the frequency fllIJ.
t12 is generated. On the other hand, the reference ea is switched as a voltage reference by a switch 25 to a constant voltage reference set by a setter 26. According to the signals 2b1 and 2b2, the constant voltage reference for PWM control and the reference 2a for RAM control are selected, and the voltage control circuit 27 and phase control circuit 28
A firing pulse is applied to the thyristor that couples the rectifier circuit 12 through the thyristor. Next, the reference 2a is applied as a frequency reference to a sine wave generation circuit 29 and a triangular wave generation circuit 30. The output signals of both circuits are compared by a comparator 31, and a switch 3
2 to the GTO that constitutes the inverter circuit 15.
Provides turn-on and turn-off pulses during M control wJ.

At this time, the switch 32 receives the signal eb1. It is operating according to eb2. During RAM control, gate pulses are generated via the oscillation circuit 33 and frequency dividing circuit 34 according to the frequency reference 2a, and turn-on and turn-off pulses are similarly applied to the GTO via the switch 32.

FIG. 10 shows an example of the main circuit of a voltage source inverter. GTO as the main switching element on the inverter side
Although this circuit is a case where a forced commutation circuit is adopted, the same effect will be obtained even if the main switching element is a thyristor, transistor, FET, etc. that has a forced commutation circuit.

FIG. 11 is a diagram illustrating output voltage waveforms during PWM control and RAM control. In the figure, (A) is the output signal of the sine wave generation circuit 29 and the triangular wave generation circuit 3o, and (B
) is the phase voltage of PWM control obtained from both signals, (,C)
is the line voltage during the same control. Also, (D) and (E) are R
These are the phase voltage and line voltage during AM control. Although not shown, since the surface control method is switched, a control circuit for synchronizing the sine wave generation circuit 29, the triangular wave generation circuit 30, and the frequency dividing circuit 34 is required.

Figure 12 shows the output voltage when switching between PWM control and PAM control. shows the relationship between and frequency chi. As shown in Fig. 11, the PNM control control amount small pulse width has a certain width determined by conditions such as the tolerance of the main switching element or control circuit, so at the switching frequency fo, the voltage change equal to the minimum pulse is occurs. For example, when switching the triangular wave frequency during PWM control, it is possible to control the fundamental wave component of the voltage so as not to make a step change, but there is a minimum pulse width between PWM control and RAM control. This always results in a step change. There would be no problem if the DC voltage could be controlled at high speed, but since it is a voltage source inverter and a smoothing capacitor, which has a large number of customers, is connected to the main circuit, there is a limit to high-speed control.

FIG. 13 is a vector diagram when the output voltage changes stepwise from ■1 to V1' when switching from PWM till in to RAM control, for example. It is determined from the primary current L1, which is a composition of the excitation current component i1d that is in phase with 2 of the secondary magnetic flux, and the torque current component 11Q that is perpendicular to the secondary magnetic flux 2, and the induced voltage e2 of the secondary magnetic flux Φ2, as Pect A ( (In the figure. Voltage drop due to leakage inductance, Rsz is voltage drop due to primary resistance)
If the primary voltage ■1 changes stepwise with the same phase, the secondary stone bundle changes from Φ2 to Φ2', although the detailed relationship is not shown.
must change.

Although it does not oscillate divergently, it changes at a relatively slow speed determined by a second-order time constant, as shown in the trajectory in the figure, which may adversely affect the entire control system or cause inrush current. This has the disadvantage that the voltage source inverter is difficult to use as a voltage source inverter.

[Object of the invention] This invention has been made to solve the above-mentioned drawbacks,
It is an object of the present invention to provide a power conversion device that can maintain the advantages of PWM control and PAM llll11 control and continue to stably operate an AC electric motor serving as a load even when switching between the two controls. Furthermore, the present invention aims to provide an economical power conversion device that can operate stably and eliminates the need to account for unnecessary capacity such as inrush current.

[Summary of the Invention] The above object of the invention can be achieved with the configuration shown below. That is, when switching from PWM control to RAM control or vice versa, the first control means that commands the speed of the AC motor to accelerate or decelerate at the time of switching.
and a second correction means for compensating for voltage phase changes.

According to this configuration, since the phase is compensated for the voltage change, all changes from V1→Vl' are compensated for by l'lq→
ZIQ', 11→jl', that is, d-d-/L(yJ-i-→L earthwork.xz-+R1z' can be changed to dt σdt, and 21d, Φ2, that is, e2 remains unchanged. Therefore, the AC motor can continue to operate stably.Furthermore, immediately before the above switching operation, a third control means for controlling the DC voltage and a third control means for commanding the speed of the AC motor is added. By using a correction means to minimize the amount of voltage change that occurs during switching,
The above action can be performed more accurately.

[Embodiment of the Invention] FIG. 1 shows a first embodiment of the invention. In the same figure, the cylinders different from those in FIG.
Acceleration/deceleration command circuit 41 receives b1, 2b2 and generates correction signal 2c for instructing acceleration/deceleration, and uses correction signal eO as reference 2a
Adder 42, PWM control, PAM control signal e
b1. In order to change the voltage phase stepwise in response to eb2, a correction signal ed for frequency increase/decrease is generated for a very short period of time.
The difference is that a phase correction circuit 43 that generates a signal ed and an adder 44 that adds the correction signal ed only to the frequency reference to obtain a new frequency reference signal ee are provided. FIG. 2 shows details of the acceleration/deceleration command circuit 41 shown in FIG.
A switch 50, which is closed when PWM control is switched to RAM control in response to f12, a resistor 51 and a capacitor 52 that constitute an integrating circuit, amplifies the integrated signal, and generates a signal eC
It consists of resistors 53, 54 and an operational amplifier 55, which generate . Further, FIG. 3 shows details of the phase correction circuit 43 of FIG. 1, and shows the signal el11. et12, a single pulse generation circuit 56 that generates a single pulse when switching from PWM control to RAM control, a setting device 57 that determines the phase correction valve, and a signal ed is generated by multiplying the respective signals. It consists of a multiplier 58.

According to the subplane circuit with the above configuration, when switching from PWM control to RAM control, step changes occur in the fundamental wave component of the voltage, which is the same as in the conventional example. acceleration signal 2c and phase correction signal 2d
occurs. 4 to 6 are diagrams for explaining this effect. That is, in FIG. 4, at time t1, P W M ! 1 fit to PA 1st l
It switches to III control, but frequency CH also changes at time t! After that, the change becomes sudden and a larger acceleration torque is required than before the switching. FIG. 5 shows a vector diagram at this time. The stepwise change in the output voltage ■1→V1' is not due to a fixed voltage phase, but due to the correction signal e(
The phase is also compensated by I. Therefore, all changes in current 11→11' flowing at that time are L1q→ztQ'
changes, and Lld is kept constant. The torque generated by the induction motor is proportional to Φ2 XJI Q, so L
A large torque can be obtained by lq-jlQ',
This torque becomes acceleration torque and can follow the frequency reference.

At time t4 in FIG. 4, P ”IV t
Switch to vl control. Similarly, the behavior at this time is
As shown in the vector diagram in the figure, it is exactly the same that Lt(I remains unchanged. However, since the stepwise change in voltage is in the decreasing direction, this phase correction signal 9d is delayed as shown in the figure. The correction is different.

The above explanation has been about correction when a stepwise change in voltage occurs. After this stepwise change is stably absorbed by acceleration and deceleration, it goes without saying that by controlling the DC voltage, the electric motor can be continued to be driven at the normal voltage and frequency ratio.

As was made clear in the explanation of the above operation, when switching from PWM control to PAM idJ 1it1 or vice versa, stepwise voltage changes are unavoidable, but it is necessary to correct the phase of the voltage and By using the generated torque as acceleration/deceleration torque, stable operation can be continued without causing fluctuations in the magnetic flux with a long time constant. Furthermore, since there is no inrush current at this time, there is no need to anticipate an unnecessary increase in current capacity.

Further, other effects can be expected from this action.

Generally speaking, systems to which such power converters are applied are often aimed at saving energy.
In such systems, the mechanical resonance point is often in the low frequency range, and the actual operating range is often in the medium to high frequency range. Therefore, by using a power conversion device with the above-mentioned function, it is possible to increase the switching frequency and reduce the enough in the frequency domain,
After avoiding the resonant frequency by PWM control, switching is performed in the acceleration/deceleration region, and no switching is performed in the normal driving region, which enables completely ideal operation.

In the above description, an example in which the phase correction circuit 43 is corrected unilaterally has been described, but the example is not limited to this. For example, it is also possible to calculate the magnetic flux axis and amount of magnetic flux from voltage, current, etc., and feed this back to adjust the voltage phase so that the magnetic flux vector does not shift.

FIG. 7 shows a second embodiment of the invention.

In the same figure, the points that differ from the first embodiment in FIG. An input limiting circuit 22 that holds, a switch 62 that similarly turns on and off in response to a single pulse e, and a constant voltage standard set by a setting device 63 via the switch 62 and a constant voltage standard set by a setting device 26. An adder 64 that adds to the voltage reference further receives the single pulse ef, and after a delay of the single pulse, performs PWM control and a PAM control signal eb.
1. The point is that a logic circuit 65 that generates eb2 is provided.

FIG. 8 shows the operation of the damper circuit constructed as described above. That is, the acceleration starts from time O, and when it reaches time tit, P
The mode is entered from WM control to PAM control control. At time tll, the comparator 24 operates as shown in (B), and a single pulse er is output from the single pulse generation circuit 61 as shown in (C). During this pulse 2r,
As shown in (A), the frequency f is temporarily held, and a constant DC voltage reference is added via the switch 62 in the direction of lowering the DC voltage. As shown in (E), the DC voltage decreases in response. During this period, the induction motor is operated at the regular voltage-frequency ratio, so the pulse width controlled by PWM control becomes narrower by the amount that the DC voltage drops, and when it is crushed, the voltage changes like a steve. can be made smaller. Time t
At 2, the RAM control signal 2b2 is output from the logic circuit 65, and the mode is switched to PAM control H. After this, the output voltage increases along the straight line (2) in (F), but the stepwise change is considerably smaller than the straight line (2) where no DC voltage adjustment is performed.

Although only the operation in the case of acceleration has been described above, the structure may be configured so that the operation in the case of deceleration is completely reversed.

From the above explanation, it can be seen that since the stepwise change in voltage is further reduced, the effect described in FIG. 1 can be obtained more accurately. The reason why the DC voltage can be controlled to be lowered between time tL1 and time t12 is because the frequency f is held and there is no voltage component required for acceleration. Therefore, as another example, it is possible to control the DC voltage below the normal tongue pressure-frequency ratio without considering the acceleration torque at all during the temporary hold, thereby further reducing the amount of change. . Also, without further temporary hold,
During this time, it is also possible to temporarily decelerate and further reduce the amount of change in voltage.

[Effect of the invention] As explained above, PAM ff is controlled by PWM control.
When switching to i control or vice versa, first correction means instructs acceleration or deceleration to the control means that instructs the speed of AC power #J at the time of switching, and second correction means to compensate for the phase of the voltage. By adding , it is possible to provide a power conversion device with the following characteristics. Furthermore, an IM for controlling the DC voltage immediately before the above switching operation.
By having a third correction means for adjusting the J 120 means and the control means for commanding the speed of the AC motorized column, that feature is realized even more precisely.

(11) It is an ideal power converter that has the characteristics of both PWM control and PAM control, that is, it has good controllability in the low frequency range and is efficient in the medium and high frequency ranges.

(2) It is a high-performance power converter that can continue stable operation even when switching between the two control methods without causing fluctuations in magnetic flux with a long time constant.

(3) Furthermore, since there is no inrush current at this time, it is an economical power converter that does not require an unnecessary increase in current capacity.

(4) (From the characteristics of 21 (31), it is possible to increase the switching frequency to a considerably high frequency, and therefore it is a power conversion device desirable for energy-saving operation that can sufficiently avoid the observational resonance frequency that exists in the low frequency region. be.

[Brief explanation of drawings]

1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a detailed diagram of the acceleration/deceleration command circuit 41 of FIG. 1, and FIG. 3 is a detailed diagram of the phase correction circuit 43 of FIG. 1. Figure 4, Figure 5,
Fig. 6 is an explanatory diagram of the operation of the first embodiment, Fig. 7 is a block diagram showing the second embodiment of the invention, Fig. 8 is an explanatory diagram of the operation of the second embodiment, and Fig. 9 is a conventional diagram. FIG. 10 is a block diagram of the device; FIG. 10 is a main circuit diagram of a voltage source inverter; FIG. 11, FIG. 12, and FIG. 13 are explanatory diagrams of the operation of the conventional device. 11... AC power supply, 12... Rectifier circuit, 15...
Inverter circuit, 16... Induced lightning #JJ machine, 22...
- Input limiting circuit, 27... Voltage control circuit, 29...
Sine wave generation circuit, 30...Triangular wave generation circuit, 33...
- Oscillation circuit, 41... Acceleration/deceleration command circuit, 43... Phase correction circuit, 61... Single pulse generation circuit, 65...
・Logic circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3, Figure 4 Figure 5 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (2)

[Claims] (1) A device for driving an AC motor by a power conversion device comprising a DC power source and an inverter circuit connected to the DC power source and converting the DC to AC, the power conversion device includes a first circuit for controlling the DC voltage. a control means, a second control means for controlling the voltage and frequency of the alternating current by pulse width modulation, a third control means for controlling the frequency of the alternating current by a minimum number of commutations, and a fourth control means for commanding the speed of the alternating current motor. Further, when switching from the second control means to the third control means as means for controlling the frequency of the alternating current or vice versa, the magnetic flux of the alternating current motor is controlled by a change in voltage generated at the time of switching. 1. A power conversion device comprising: a first correction means for instructing a fourth control means to accelerate or decelerate at the time of switching, and a second correction means for compensating for voltage phase changes so as not to fluctuate. (2) In a device for driving an AC motor by a power conversion device comprising a DC power source and an inverter circuit connected to the DC power source and converting the DC to AC, the power conversion device includes a first circuit for controlling the DC voltage. a control means, a second control means for controlling the voltage and frequency of the alternating current by pulse width modulation, a third control means for controlling the frequency of the alternating current by a minimum number of commutations, and a fourth control means for commanding the speed of the alternating current motor. further comprising a control means for controlling the frequency of the alternating current, from the second control means to the third control means;
Or, when switching in the opposite direction, the amount of change in voltage is controlled via the first and fourth control means immediately before switching so that the magnetic flux of the AC motor does not fluctuate due to the change in voltage that occurs at the time of switching. A power conversion device comprising a third correction means for adjusting, a first correction means for instructing the fourth control means to accelerate or decelerate at the time of switching, and a second correction means for compensating for a voltage phase change. Device.