JPH0245439B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention detects a point that is moved by a certain electrical angle from a point where the magnitude relationship of voltages of arbitrary two adjacent phases in a multiphase AC circuit changes. This invention relates to a synchronization signal detection circuit.

[Prior art and its problems]

The most common types of polyphase AC circuits are 3.
There is a phase AC circuit. The so-called VVVF inverter converts the 3-phase AC power from this 3-phase AC circuit into DC using a rectifier, and then converts it into variable voltage/variable frequency AC power so that the induction motor can be operated at a desired speed. is frequently used. When it is desired to slow down or stop this induction motor, electrical braking is applied, but from the standpoint of energy conservation, so-called regenerative braking converts the kinetic energy held by this motor into electrical energy and returns it to the three-phase AC circuit. For this purpose, an inverter made of a switching element such as a transistor is connected in parallel with the above-mentioned rectifier to provide the above-mentioned regenerative braking.

Figure 1 is a circuit diagram showing an example of a VVVF inverter capable of regenerative braking, in which the first phase is 1, the second phase is
A three-phase AC circuit is formed by the second phase (2) and the third phase (3), and the three-phase AC power from this circuit is converted into DC power by the rectifier 30. This DC power is applied to a motor side inverter 32 made of a transistor through a smoothing capacitor 31, and the induction motor 33 is operated at a desired speed by the variable voltage/variable frequency AC power outputted by the motor side inverter 32. When operating this motor 33 in regenerative braking mode, each arm U, V, W, X, Y, Z of a power supply side inverter 34 composed of transistors connected in parallel to a rectifier 30 is connected to a three-phase AC circuit. Power is returned to this three-phase AC circuit by turning it on and off in synchronization with the voltage phase of each phase 1, 2, and 3. Reference numeral 35 denotes a current limiting resistor for suppressing inrush current from flowing while the power supply side inverter 34 is in operation.

In order to return power from the DC side to the AC power supply side using an inverter using semiconductor switching elements such as transistors, the power supply side inverter 34 is switched in synchronization with the moment when the magnitude relationship between the voltages of two adjacent phases of the AC power supply is switched. The base of the transistor in the arm corresponding to that phase is driven to turn it on or off. However, if the transistor is operated at the instant when the magnitude relationship between the voltages of two adjacent phases changes, there is a risk of accidents such as arm short circuits, so in reality, the moment when the magnitude relationship between the voltages of the two adjacent phases changes. As a starting point,
The corresponding transistor is turned on with a slight time delay from that moment, and then this transistor is turned off just before the magnitude relationship with the voltage of the next phase changes, giving the synchronization signal a dead zone.

By the way, when a semiconductor switching element or the like is connected to an AC power source and operated, the power supply voltage waveform becomes a distorted waveform due to voltage collapse and vibration caused by this, causing problems. Therefore, in order to correct such waveform distortion, a filter is inserted into the above-mentioned synchronization signal detection circuit, but this filter causes a phase delay in the synchronization signal itself, so it is difficult to insert the filter. It has the following drawback.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a synchronization signal detection circuit that can detect a synchronization signal having a stable dead zone even if the waveform of an AC power supply voltage is distorted.

[Key points of the invention]

In this invention, a filter is connected to the synchronization signal source to correct voltage waveform distortion, and the phase delay caused by this filter is corrected by a phase shifter, thereby obtaining a synchronization signal with a required dead zone. However, this phase shifter is configured to use a comparator to compare the magnitude relationship between the voltage obtained by dividing the voltage of a certain phase using a voltage divider and the voltage of an adjacent phase.

[Embodiments of the invention]

FIG. 2 is an explanatory diagram showing the principle of the present invention in a three-phase AC circuit, and the content of the present invention will be explained in detail below with reference to FIG.

In FIG. 2, the voltage waveform of the first phase of the three-phase AC circuit is shown by the solid line A1, and the voltage waveform of the second phase adjacent to this first phase is shown by the solid line B1. The magnitude relationship of the voltage of the second phase changes at point P, but if the voltage waveform is distorted as described above, a filter is inserted to correct this waveform distortion. In FIG. 2 as well, the voltage waveform A1 of the first phase has waveform distortion, but due to the effect of the filter, it becomes a voltage waveform A2 without distortion. Similarly, the voltage waveform B1 of the second phase obtains a distortion-free voltage waveform like waveform B2 by the filter connected to this phase, but if the filters have the same time constant for both the first and second phases, the waveform A2 is delayed by θ ₁ in electrical angle with respect to waveform A1, and waveform B2 is similarly delayed by θ ₁ with respect to waveform B1. Therefore waveform A
Assuming that the point where the magnitude relationship between waveform B2 and waveform B2 changes is point Q, this point Q will have a phase delay of θ ₁ from the above-mentioned point P.

When the peak value of the phase voltage of the first phase and the second phase is E, if a voltage divider is connected to the load side of the above-mentioned filter and this first phase voltage is divided by a voltage division ratio k, the waveform We obtain a voltage waveform A3 whose high value is kE, which is shown by a broken line, but since the phase of this waveform A3 is delayed by θ ₁ due to the filter, the waveform A3
is in phase with waveform A2. Therefore, if the point where the magnitude relationship between this divided voltage waveform A3 and the aforementioned second phase waveform B2 switches is the point R, this point R will lead the phase by θ ₂ in electrical angle than the aforementioned Q point. Located in
This θ ₂ can be expressed by the following equation (1).

θ ₂ =tan ⁻¹ (1−k/1+ktanφ) (1) Here, φ is an angle determined by the number of phases of the AC voltage, and in the case of three-phase AC, φ=π/6. Since both φ and voltage division ratio k in equation (1) above are constant values that are unrelated to voltage and frequency, the angle θ ₂ can be determined only by voltage division ratio k, regardless of voltage and frequency. can.

If the value of θ ₂ obtained from the above equation (1) is set to an appropriate value larger than the delay θ ₁ due to the filter described above, the point R, which is the intersection of waveform B2 and waveform A3, can be changed to waveform A1. The position can be advanced from the point P, which is the intersection of the waveform B1 and the waveform B1. If the phase difference between point P and point R is θ, then θ=θ ₂ −θ ₁ =tan ⁻¹ (1−k/1+ktanφ)−θ ₁
...(2) becomes. Here, θ ₁ is a known value that can be obtained from the time constant of the filter, so the first and second phases
The point advanced by θ from the P point where the phase voltage relationship changes is found from equation (2), and a synchronization signal with this θ as the dead zone can be obtained, but if it is a three-phase AC circuit, then Similarly, synchronization signals having dead zones of θ are obtained for the second phase and the third phase, and for the third phase and the first phase. Furthermore, by using a timer or the like to elapse a time corresponding to the electrical angle of θ + α from this point R, α
A synchronization signal with a dead zone of electrical angle is obtained.

FIG. 3 is a circuit diagram showing an embodiment of the present invention based on the above-described principle, and shows the case of a three-phase AC circuit. In FIG. 3, 1 is the first phase of a three-phase AC power supply, and the voltage of this first phase is input to the comparator 7 via a filter 4F. Similarly, the voltages of the second phase 2 and the third phase 3 of the three-phase AC power supply are
Comparators 8 and 9 via filters 5F and 6F, respectively.
is being entered. Here filters 4F, 5F, 6
For example, as shown in the figure, F is a filter consisting of a resistor and a capacitor, which corrects the waveform distortion of each phase voltage _.
As already explained, a phase delay occurs.

Each phase voltage obtained through these filters 4F, 5F.
The voltage is divided by R and 6R at a voltage division ratio of k, and the voltage obtained by dividing the voltage from the first phase 1 through the filter 4F and the voltage divider 4R is input to the comparator 8, and the voltage obtained by dividing the voltage from the first phase 1 through the filter 5F is divided. The voltage obtained from the voltage regulator 5R is sent to the comparator 9, and from the third phase 3 to the filter 6.
The voltage obtained by the voltage divider 6R via F is input to the comparator 7. Considering this regarding the comparator 7, this comparator 7 has a filter 4F.
The voltage of the first phase 1 that has passed through the filter 6F and the voltage of the third phase 3 that has been divided by the voltage divider 6R are input, and the point where the magnitude relationship of these two voltages changes, that is, R in FIG. A point is detected, which is an electrical angle θ ahead of the point where the magnitude relationship between the voltage of the first phase 1 and the voltage of the third phase 3 changes, that is, the point P in FIG. 2. This also applies to comparators 8 and 9. These comparators 7,
The output signals from 8 and 9 are sent to logic circuits 13 and 15.
The output signal from the logic circuit 13 is given as θ+α in electrical angle by the timer 14.
Outputs a time-delayed signal corresponding to . Since the output from this timer 14 is input to the logic circuit 15, each arm U, V,
The transistors that make up W, X, Y, and Z are turned on.
This control signal sends an OFF control signal, but this control signal issues an ON signal with a delay of α in electrical angle from the point where the magnitude relationship of each phase voltage of the 3-phase AC power source changes, and θ
Since the off signal will be issued as soon as possible, the difference between θ +
A synchronization signal having a dead zone with a width α is formed to prevent the inverter from causing an accident such as an arm short circuit. The time corresponding to this dead zone θ+α is set by the timer 14, but since this time is a very short value, even if the voltage or frequency changes, the influence on the set time is small.

FIG. 4 is an operational waveform diagram according to an embodiment of the present invention. Waveforms A1 and B indicated by solid lines in FIG.
1 and C1 are the first and second phases of a three-phase AC circuit, respectively.
These are the waveforms of the power supply voltages of phase and third phase, and the waveforms A2, B2, and C2 shown by one-dot chain lines are voltage waveforms with a phase delay of θ ₁ due to the filter, and the waveforms A3, B3, and C3 shown by broken lines are This is a voltage waveform obtained by dividing waveforms A2, B2, and C2 using a voltage divider at a voltage division ratio of k. In order to turn on and off the transistor in arm U of the transistor inverter 34, the comparator 7 detects the intersection of the waveform A2 and the waveform C3.
The timer 14 may be turned on after a time corresponding to θ+α in electrical angle has elapsed from this intersection, the comparator 8 may detect the intersection of waveform B2 and waveform A3, and it may be turned off at this detection point. , 40 are control signals for arm U. Other arms V, W,
The same applies to X, Y, and Z.

FIG. 5 is a circuit diagram showing a second embodiment of the present invention, which differs from the embodiment shown in FIG.
The comparators 10, 11, 12 are added, the timer 14 is deleted, and the filter 4F connected to the first phase 1, second phase 2, third phase 3, and each phase , 5F, and 6F, the voltage dividers 4R, 5R, and 6R, which are also connected to each phase, and the logic circuits 13 and 15, their names, uses, and functions are the same as in the embodiment shown in FIG. Explanation will be omitted.

In FIG. 5, the comparator 10 receives the voltage that has passed through the filter 4F of the first phase 1 and the voltage that has passed through the filter 5F of the second phase 2.
Since the voltage passing through F is input, the intersection of both voltages becomes point Q in Fig. 2, and from point P, θ ₁
It is possible to detect points whose phase lags by an electrical angle of
If this Q point is used as a transistor ON signal, a synchronization signal having a dead zone of θ ₁ can be obtained. Based on the same idea, comparators 10, 11, and 12 are newly provided with voltages with a voltage division ratio different from the conventional voltage division ratio k.
The electrical angle of the dead zone of the delay can be freely changed without using the timer 14 by inputting the following information.

〔Effect of the invention〕

In this invention, by inserting a filter into the circuit in order to correct the distortion of the voltage waveform of the multiphase AC circuit, even if the intersection point of each phase voltage shifts due to the influence of the time constant of the filter, the voltage waveform of the multiphase AC circuit can be corrected. By inputting a combination of the divided voltage and each phase voltage to a comparator, a point in time is advanced by an electrical angle determined by the voltage division ratio of the voltage divider with respect to the point in time when the magnitude relationship between the power supply voltages switches. Alternatively, a delayed point can be detected. Since this electrical angle of delay or lead is always constant regardless of frequency fluctuations or voltage fluctuations, the phase delay due to the filter is added or subtracted from it and used as a control signal to turn on and off each arm of the inverter. For example, since a stable synchronization signal with a dead zone that is not affected by voltage or frequency fluctuations can be obtained, the width of the dead zone can be more accurate than when using a timer or the like. Therefore, for example, when DC power is returned to an AC power source as in regenerative braking, each arm of the inverter is turned on and off as long as the width of the dead zone of the synchronization signal does not change due to disturbances as described above. There is no risk of arm short-circuiting due to overlapping on-operations, and the returned power does not fluctuate.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a VVVF inverter capable of regenerative braking, Fig. 2 is an explanatory diagram showing the principle of the present invention in a three-phase AC circuit, and Fig. 3 is a circuit diagram showing an embodiment of the present invention. It is. FIG. 4 is an operational waveform diagram according to an embodiment of the present invention, and FIG. 5 is a circuit diagram showing a second embodiment of the present invention. 1...First phase, 2...Second phase, 3...Third phase,
4F, 5F, 6F...Filter, 4R, 5R, 6
R... Voltage divider, 7, 8, 9, 10, 11, 12...
...Comparator, 13, 15...Logic circuit, 14...
...Timer, 30... Rectifier, 31... Smoothing capacitor, 32... Motor side inverter, 33... Induction motor, 34... Power supply side inverter, 35...
Current limiting resistor, 40...Control signal for arm U,
U, V, W, X, Y, Z...Power supply side inverter 3
4 each arm.

Claims (1)

[Claims] 1. In a synchronization signal detection circuit that compares the voltages of two adjacent phases of a multiphase AC circuit and detects the point where the magnitude relationship between the two voltages changes,
A filter connected to each phase of the multiphase AC circuit to correct voltage waveform distortion, a voltage divider connected to the load side of the filter in any phase, and a voltage divided by the voltage divider and 1. A synchronous signal detection circuit comprising: a comparator that compares a voltage on a load side of the filter in a phase adjacent to a phase to which a voltage divider is connected.