JPH01234096A - Method and device for restarting current type inverter after power failure - Google Patents

Abstract

PURPOSE:To restart automatically, upon recovery from instantaneous power interruption, with no commutation failure even when there is a residual voltage, by detecting the phase of terminal voltage of a load motor and resuming firing with such firing phase as the phase of current lags from that of voltage. CONSTITUTION:Upon occurrence of power interruption, a state signal (h) indicating the initial (commutation phase concerning to resumption of commutation is transmitted from a ring counter 15 to a signal selector 21. On the other hand, terminal voltage of a motor 5 is provided through a potential transformer 8 to a phase detector 20, then a signal indicating that the voltage phase thereof has reached to a preset value is transmitted to the signal selector 21. The signal selector 21 selects one corresponding to the initial commutation phase according to the signal (h) fed from the ring counter 21 and transmits the selected signal (g) to a ring counter 15. The ring counter 15 resumes commutation upon receipt of the output signal (g) from the signal selector 21.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method and device for restarting a current source inverter after a power outage, and is particularly applicable to restarting a current source inverter when residual voltage remains in the load motor. Concerning what is suitable.

[Conventional technology]

Conventionally, the following restart has been known as described in Japanese Unexamined Patent Publication No. 59-14392.

In general, inverter-driven electric motors used in textile machinery, water supply and sewage systems, etc. are required to continue operating even if a power outage occurs for less than a few seconds, and to return to the specified operating state immediately after power is restored. It is often done. In this case, it goes without saying that care must be taken to ensure that the inverter device itself that performs such control is also safely protected. Therefore, the inverter operation is stopped immediately after a momentary power failure is detected, and the electric charge in the commutation capacitor is held, and in the event of a power failure, power is restarted from the same thyristor that was used when the power failure was stopped.

[Problem to be solved by the invention]

The above conventional technology is suitable when the power is restored and restarted after the power outage is relatively long and the residual voltage of the motor disappears, but when the power is restored and the power is restarted after the power outage is short and the residual voltage of the motor is large. If this happens, it may not be possible to restart normally. This is caused because the inverter output current and voltage phase at the time of restart do not match the residual voltage phase of the motor, which causes a problem such as failure of commutation.

For example, depending on the phase relationship between the ignition phase related to the initial rotational flow phase at the time of restart and the residual voltage phase of the motor, the charging voltage of the commutator capacitor related to the next rotational flow phase may become insufficient.
As a result, commutation may fail because the necessary reverse bias time cannot be secured.

An object of the present invention is to provide a method and apparatus for restarting a current source inverter after a power outage, which can prevent commutation failure due to residual voltage of a load motor.

[Means to solve the problem]

In order to achieve the above object, the restart method of the present invention provides an initial rotational current when restarting the ignition control of a current-source inverter that has been stopped based on a power outage signal with a motor as a load based on a power outage recovery signal. The phase of the terminal voltage of the load motor related to the phase is detected, and the ignition control is restarted at the ignition phase in which the current related to the initial rotation flow phase is at least in a phase lagging behind the phase of the voltage.

Further, the restart device according to the present invention is a current inverter comprising a starting control means for stopping the starting control of a current source inverter whose load is an electric motor in response to a power outage signal, and restarting the starting control based on a power outage recovery signal. In the restart device after a power outage, the phase detection means detects a physical quantity representing the phase of the terminal voltage of the electric motor, and among the detected physical quantities, one related to an initial rotational flow phase at the time of restarting matches a predetermined value. A restart timing determining means is provided for detecting this and outputting an ignition restart command to the ignition means.

[Effect]

First, the principle of the present invention will be explained using FIGS. 2 to 4. Figure 2 shows the commutation equivalent circuit from U phase to V phase, and the 3rd
The figure shows the operating waveforms during commutation.

As shown in those figures, during the conduction delay period T, the switch S is closed and S2 is open, and the commutating capacitor CC is charged at a constant current with the DC current ID. At this time, the commutating capacitor voltage ec is expressed by the following equation.

I.

ec=-t-Ec (1)c Here, Ec is the charging voltage of the commutating capacitor before commutation. The time Tc for reverse biasing the thyristor is determined as n from the above equation and the condition that the commutating capacitor voltage becomes zero. If this reverse bias time Tc is not longer than the turn-off time of the thyristor, the thyristor cannot be turned off and commutation will fail. Therefore, the pre-commutation charge voltage Cc of the commutation capacitor Cc needs to have a value equal to or greater than a predetermined value depending on the current ID at that time.

Note that the conduction delay period continues until the commutating capacitor is further charged and becomes equal to the voltage υ between the terminals UV. As shown in the figure, if the voltage phase at this point is φ, and the actual value of the voltage between the terminals is VM, then the conduction delay time T□ is calculated by the formula (2
), we can find D.

On the other hand, the voltage ec of the commutating capacitor CC is at the terminal U of the motor.
, V, the switch S2 closes and a commutating period begins. The initial voltage of the commutating capacitor is V
M sinφ, and if we also ignore the change in motor voltage during the commutation type period for simplicity, the relational expression between voltage and current at this time is the following equation (4).
become that way.

dt dttl uv=
22 VM Sinφlu+1v=In By rearranging the above equation (4), the following equation is obtained.

Initial condition=+0. Using iu=■D, formula (5)% formula% (6) is obtained. Further, the commutating capacitor voltage ec is expressed as follows.

Since the commutation type time T2 is the time until lu becomes zero, it is obtained from equation (6). Moreover, the charging voltage of the commutating capacitor at this time becomes a linear equation.

c Here, the phase φ at which the commutation type period begins corresponds approximately to the power factor angle of the electric motor.

The charging voltage Ec of the commutation capacitor in equation (9) is used for the next commutation. Therefore, if the power outage is long and there is no residual voltage in the motor, the second term will be 0 and commutation will continue. However, if the power outage time is short or the decay time constant of the residual voltage of the motor is long, the second term cannot be ignored.
When sinφ is negative, commutation becomes more difficult than when there is no residual voltage.

This will be explained in detail with reference to FIG.

The figure shows the transition of the commutation capacitor voltage eG due to commutation. For each three-phase commutating capacitor, before the first rotational flow, 8Ct related to the initial rotational flow phase is -Ec, ec related to the next rotational flow phase,
ec3 related to the 09th quadratic flow phase is charged to 10 Ec (for convenience of explanation, the polarity is reversed from that in FIG. 3). As a result of commutation, if the first rotational flow phase is charged to 10E'c, the next rotational flow phase changes to (E c + E'c)/2, and the successive rotational flow phases change to (Ec E''C)/2. As a result, when E'c<Ec, the DC current 1o must be reduced from the first time in order to make the reverse bias time Tc shown in equation (2) sufficiently long during the next rotation.However, this If you do this repeatedly, you will eventually become unable to drive.

From the above commutation operation, in order to ensure commutation even when there is residual voltage, the timing of the initial rotation flow is important, and the end timing of the conduction delay time T□ is shown in Figure 3. Alternatively, as shown in FIGS. 4(a) and 4(c), it can be seen that it is necessary to perform control so that the phase lags behind the phase of the motor terminal voltage.

In other words, as shown in Figure 3, the switch S involved in commutation
If the output of the ignition signal to the switch S2 is resumed at the timing when the rising phase of the current of 2 is in the lag region with respect to the phase of the terminal voltage υuv, it will be sufficient as shown in Fig. 4 (a) and (c). Therefore, it is possible to secure a charging voltage Ec.

According to the device of the present invention, an ignition restart command is output when a physical quantity representing the phase of the terminal voltage of the motor, which is related to the initial rotation flow phase at the time of restart, matches a predetermined value. The inverter is restarted.

The above-mentioned predetermined value is set in consideration of the conduction delay time T□ in advance so that the current phase related to the initial rotation flow phase lags behind the phase of the corresponding terminal voltage.

Further, as the physical quantity representing the voltage phase, in addition to the phase itself, the level of the instantaneous voltage υuv, etc., the time from the zero point of the instantaneous voltage υuv, etc. can be applied.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows an overall configuration diagram of a current source inverter device according to an embodiment to which the present invention is applied.

As shown in the figure, the current source inverter device of this embodiment includes an AC power source 1, a rectifier 2, a DC reactor 3, an inverter 4,
AC motors such as induction machines5. Alternator 6. Transformer 7, 82
Frequency command device 9, command converter 10, voltage regulator 11, current regulator 12, pulse phase shifter 13, voltage/frequency (V/
F) Converter 14, ring counter 15, power failure detector 16
．． Current detector 17, current/voltage waveform shaping circuit 18, 1
9, and these have the same functions and configuration as the conventional ones.

A phase detector 20 which is connected to the secondary side of the transformer 8, detects the phase of the terminal voltage, and outputs a signal when the detected phase matches a predetermined value;
A signal selector 21 selects the output signal of the phase detector 20 based on a signal indicating the initial rotational flow phase inputted from the ring counter 15, and outputs a restart timing signal to the ring counter 15. Note that a part of the 1-phase detector 20 and the signal selector 21 form restart timing determining means.

The operation will be explained below.

In normal conditions, the magnitude of the motor current is determined by comparing the signal C obtained as the output of the voltage regulator 11 and the current signal e detected by the current transformer 6 and its shaping circuit 18.
The result is calculated by the current regulator 12, and the pulse phase shifter 13
It is controlled by controlling the phase of the rectifier 2 via the rectifier 2. On the other hand, the motor frequency is controlled by applying the frequency command obtained from the frequency command device 9 through the command converter 10 to the inverter 4 through the V/F converter 14 and the ring counter 15, and controlling the firing period. Ru.

Operations during power outage and power outage recovery will be explained with reference to FIG. Now, if the AC power supply 1 fails at time t□, the voltage transformer 7
Since the secondary voltage of becomes zero, the power failure detector 16 detects this and sends the output signal a to the pulse phase shifter 13 and the voltage controller 1.
1. Notify ring counter 15. The pulse phase shifter 13 immediately stops its output signal d (called suppression), the voltage controller 11 sets its output signal C to a level equivalent to zero current, and the ring counter 15 stops its output signal d (called suppression). call) and stop counting the pulses,
The state of the commutation phase at that time is maintained.

In this state, when the AC power supply 1 recovers from the power outage at time t2, a predetermined voltage is applied to the power outage detector 16 via the voltage transformer 7, and its output signal a becomes the power outage recovery signal. The counter 15 starts outputting pulses again (signals 1, d).

The output signal C of the voltage controller 11 once increases to a predetermined current value, and then becomes a command to gradually increase the current value.

However, in general, a predetermined current level is required for commutation, so commutation is performed by the current detector 17 when the signal e obtained through the current transformer 6 and the waveform shaping circuit 18 rises to a predetermined value. (at time t3), and resumes at time t4 after transmitting the detection signal f to the ring counter 15 (signal d')
. If the timing of commutation restart is not appropriate, the above-mentioned commutation failure will occur. Conventionally, the process was restarted at time t3.

Here, the restart of this embodiment will be explained.

After the power outage occurs at time t1, the ring counter 15 transmits a status signal indicating the initial rotational flow phase for restarting commutation to the signal selector 21. On the other hand, the terminal voltage of the motor 5 is applied to the phase detector 20 via the transformer 8.

A detection signal g indicating that the voltage phase has reached a predetermined value is transmitted to the signal selector 21. Among these signals, the signal selector 21 selects the one corresponding to the initial rotation flow phase according to the signal from the ring counter 15,
It is transmitted to the ring counter 15 (signal g). The ring counter 15 receives the output signal g of the signal selector 21 at t4.
Commutation resumes at some point.

FIG. 6 shows an example of a specific configuration of the phase detector 20, and FIG. 7 shows its operating waveforms. The instantaneous value of the motor voltage transmitted via the transformer 8 is compared with a predetermined level ■S by a comparator 101 for each phase, and is further set in an increasing direction (or a decreasing direction depending on the predetermined phase) by a differentiator 102. The path/L/path has a predetermined width, and the signals UP, VP, and W are respectively output.
P.UN.

They are output as VN and WN. Among these, selector 2
1, one signal corresponding to the initial rotation flow phase signal of the ring counter 15 is selected. The selector 21 can be configured with an IC called a multiplexer. The comparison voltage vS is determined in consideration of the conduction delay time T□, and is usually between o-vp. In this case, setting Vp to a constant value regardless of the motor voltage (referred to as normalization) increases the accuracy of setting Vs. The following methods (i) to (city) are known as such methods.

(1) −Arithmetic unit with lag characteristic (gain is (1+(ω/ω)
C) 2), so the lower the frequency, the higher the gain) (il) Power supplies vCC and -VccL that create the comparison voltage vS
, knee Vp and -VP method (ui) Passing Vp through a divider "(V cc / V P
, and then multiply it with the original signal using a multiplier to match its peak to Vcc.Also, instead of the method using Vs above, a timer can be used to output a signal UP after a predetermined time from the zero point of the motor voltage.
There is also a method of making the time variable in proportion to the period of the voltage waveform and outputting a signal after a predetermined electrical angle. Needless to say, the selection must be made depending on the allowable range of settings due to differences in accuracy and frequency.

That is, 2"VMsinψ of the second term of equation (9) above
In addition to determining how many volts or more the conduction delay period T0 should be, correction of the conduction delay period T0 (the electrical angle is inversely proportional as the time is constant regardless of the frequency)
An appropriate method will be selected to achieve this over the actual residual voltage and frequency range.

〔Effect of the invention〕

As explained above, according to the present invention, when restarting the ignition control of a current source inverter that has been stopped based on a power outage signal and has a motor as a load based on a power outage recovery signal, The phase of the terminal voltage of the load motor is detected, and ignition is restarted at an ignition phase in which the current related to the initial rotation flow phase lags at least the phase of the voltage. Automatic restart can be performed without commutation failure even when there is residual voltage in the motor, so even if the power outage is short or the decay time constant of the residual voltage in the motor is long, restarting can be performed smoothly. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the device according to the present invention;
2, 3, and 4 are operation explanatory diagrams regarding the principle of the present invention, FIG. 5 is an operation explanatory diagram of the embodiment shown in FIG. 1, and FIG.
The figure is a configuration diagram of a specific example of the main part of the embodiment in Figure 1, and Figure 7 is a configuration diagram of a specific example of the main part of the embodiment in Figure 1.
It is an explanatory diagram of the operation of the figure. 4... Inverter, 5... Electric motor, 15... Ring counter, 16... Power failure detector, 20... Phase detector, 21... Signal selector. Figure 1 1 ゛Electric switch# 15: Tsunku゛Kausoku 2: i-koshi disruptor 16
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Claims (1)

[Scope of Claims] 1. When restarting the ignition control of a current source inverter which has been stopped based on a power outage signal and has been stopped based on a power outage signal, based on a power outage recovery signal, the terminals of the load motor related to the initial rotation flow phase are A method for restarting a current source inverter after a power outage, which detects the phase of the voltage and restarts ignition at an ignition phase in which the current related to the initial rotation flow phase lags at least the phase of the voltage. 2. In a current inverter restarting device after a power outage, the current inverter restarting device has an ignition control means that stops the ignition control of a current source inverter whose load is an electric motor in response to a power outage recovery signal, and restarts the ignition control based on the power outage recovery signal. phase detection means for detecting a physical quantity representing the phase of the terminal voltage of the motor; and detecting that one of the detected physical quantities relating to the initial rotational flow phase at the time of restarting matches a predetermined value, and the ignition is started. A restart device for a current source inverter after a power outage, the device comprising restart timing determining means for outputting an ignition restart command to the means.