JPH0698544A - Multiplexed voltage type inverter - Google Patents

Abstract

(57) [Summary] [Objective] The control power supply 10 that outputs a DC voltage according to a voltage command, and a plurality of inverters 13a and 13b that convert the DC voltage into AC voltages having different phases are provided. Restarting the multiplexed voltage source inverter which drives the AC electric motor 15 by the combined voltage of AC voltages having different phases so that an overcurrent does not flow. Configuration: Means 25, 26, 30, 27 for controlling the phase of the AC voltage of each of the plurality of inverters according to the voltage ratio between the DC voltage and the voltage of the AC motor are provided, and the inverter 25 is provided in an abnormal situation. -When the operation of the inverter is stopped, the voltage command is held and the frequency command is changed in accordance with the rotation speed of the AC motor, and when the operation of the inverter is restarted, the above-mentioned voltage ratio is changed according to the voltage ratio at that time. Controls the phases of the AC voltages of a plurality of inverters and holds the frequency command, and returns the voltage command and the control phase to a normal operating state for a predetermined time, and then returns the frequency command to a normal operating state. To return to the preset frequency
Provide 28 and 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex voltage source inverter for driving an AC motor, and more particularly to a multiplex voltage source inverter for smooth restart.

[0002]

2. Description of the Related Art FIG. 3 (A) shows a multiplexed voltage source inverter for variable speed driving of an AC motor such as an induction motor.

This device comprises a converter 10 and a reactor 1
1. The so-called so-called DC voltage obtained by the capacitor 12 is converted into two three-phase AC voltages having different phases by the two inverters 13a, 13b and combined by the transformers 14a, 14b to drive the AC motor 15. , A 12-pulse inverter, is a multiplexed voltage source inverter.

When the switch RUN is turned on by the operation command, the setting signal of the frequency setter 16 is input to the change rate limiting circuit 17 and the frequency reference f ^{* is set.} Rises to a set value at a predetermined rate of change, and the voltage reference V at a predetermined voltage / frequency is passed through the function unit 18.
^* Occurs. This voltage reference V ^* Is compared with the DC voltage V _{dc of the} capacitor 12 detected by the voltage detector 20, and the voltage controller 19 controls the converter 10 according to the deviation value. As a result, the DC voltage V _dc is the voltage reference V ^*. Is controlled to a value corresponding to.

On the other hand, the frequency reference f ^* Is converted into a phase signal θ through an integrator 21 and converted into a drive signal having a phase difference of 30 degrees by a pulse distribution circuit 22 and the inverters 13a and 13b.
Drive each. As a result, the inverters 13a, 13b
AC voltage with a phase difference of 30 degrees is output from the transformer 14
The phase difference is canceled by a and 14b, and the secondary side voltage is added and combined. As a result, an AC voltage having a 12-pulse waveform is supplied to the AC motor 15, and the AC motor 15 enters the operating state.

When the switch RUN is turned off by the stop command, the signal of the frequency reference setting unit 16 input to the rate-of-change limiting circuit 17 is cut off and the output signal of the PLL circuit 24 is input instead. The PLL circuit 24 compares the phase of the terminal voltage (motor voltage) of the AC motor 15 detected by the voltage detector 23 with the phase signal θ and outputs the control signal f so that the phase difference becomes zero. As a result, the frequency reference f ^* Changes according to the rotation speed of the AC motor 15. When the switch RUN is off, the change rate limiting function of the change rate limiting circuit 17 is disabled and the tracking characteristic of the PLL circuit 24 is improved.

[0007]

In the conventional device described above, when an instantaneous power failure occurs and the power is restored, or when a minor failure occurs and automatic reset and restart are performed, an overcurrent flows to the AC motor 15 and stops. However, there is a problem that the operation cannot be continued stably. The operation when such a state occurs will be described with reference to FIG.

If a momentary power failure or a minor failure occurs at time t ₁ , the switch RUN is turned off by the stop command and the operation of the inverters 13a, 13b is stopped. Therefore,
The rotation speed of the AC motor 15 begins to decrease, and the frequency f of the motor voltage detected by the PLL circuit 24 decreases as shown in FIG. 3 (B). In addition, the motor voltage V decreases faster than the decrease rate of the frequency f because the exciting magnetic flux weakens. Further, during this time, the load of the capacitor 12 is not discharged, so that the DC voltage V _dc maintains the voltage at the time t ₁ . If the motor voltage V and the DC voltage V are restarted by a power recovery or an automatic reset at time t ₂ during such a state change.
Since the ratio of _dc is shifted greatly, excessive current I _m flows in the AC motor 15, inverter - can not be safely restarted the operation of the motor.

The present invention has been made to solve the above problems, and its purpose is to change the phase of the AC voltage output by each inverter when the inverter is restarted. Therefore, it is an object of the present invention to provide a multiplexed voltage type inverter which can promptly eliminate the deviation between the motor voltage and the DC voltage without causing an overcurrent and can restart safely.

[0010]

To achieve the above object, the present invention converts a control power source for outputting a DC voltage according to a voltage command and the DC voltage into AC voltages having different phases. In a multiplex voltage source inverter having a plurality of inverters, which drives an AC electric motor by a combined voltage of AC voltages having different phases, in the above-mentioned voltage converter according to the voltage ratio between the DC voltage and the voltage of the AC electric motor. A means for controlling the phase of each AC voltage of the plurality of inverters is provided, and when the operation of the inverter is stopped in an abnormal situation, the voltage command is held and the frequency command follows the rotation speed of the AC motor. Change and restart the operation of the inverter,
The frequency command is held together with controlling the phases of the AC voltages of the plurality of inverters according to the voltage ratio at that time, and the voltage command and the control phase are returned to a normal operating state for a predetermined time, and thereafter. Means is provided for returning the frequency command to the normal operating state and returning to the set frequency.

[0011]

When the operation of the inverter is stopped in an abnormal situation, the rotation speed of the AC motor starts to decrease and the voltage ratio between the DC voltage and the voltage of the AC motor starts to change. After that, when the operation of the inverter is restarted, the phase of the AC voltage of the plurality of inverters is controlled according to the voltage ratio at that time, and the DC voltage is combined with the AC motor without causing an overcurrent by combining the voltage vectors. The voltage command and the control phase are returned to the normal operating state for a predetermined time, and are returned to values corresponding to the frequency command holding the DC voltage and the voltage of the AC motor.
After that, the frequency command is returned to the normal operating state, the frequency is returned to the set frequency at the normal rate of change, and the engine is smoothly restarted.

[0012]

FIG. 1 shows an embodiment in which the multiplexed voltage source inverter of the present invention is implemented by using two sets of inverters.

In FIG. 1, the divider 25 calculates the ratio (K = V / V _dc ) between the DC voltage V _dc and the motor voltage V. The function unit 26 outputs a function value φ ₁ of cos ⁻¹ K. The pulse distribution circuit 27 has a conventional function of outputting two inverter drive signals having a phase difference of 30 degrees in accordance with the phase signal θ, and further has an input terminal for a signal φ ₂ which freely changes the phase difference. Is equipped with. The rate-of-change limiting circuit 28 sets the frequency command f ^* at a predetermined rate of change until the set frequency reference is reached ^. Is changed to form the closed loop of the PLL circuit 24, the change rate limiting function is invalidated. Further, the frequency command f ^{* is} generated by the external command s ₁ ^. Has the function of temporarily holding.

The hold circuit 29 receives a temporary voltage reference V ^* according to an external command * RUN ^. It has a function to hold a and usually functions as a buffer. When the external command s ₁ is input, the output unit 30 outputs a signal φ ₂ which becomes zero at a predetermined attenuation rate with the input value φ ₁ from the function unit 26 as the maximum value. The other elements that are the same as those in FIG. When the multiplexed voltage source inverter of the above construction is operating normally, the external command s ₁ is not given and the output signal φ ₂ of the output section 30 is zero.

The external command * RUN is turned off and
The field circuit 29 acts merely as a buffer. Therefore, the signal φ ₂ for controlling the phase difference is not input to the pulse distribution circuit 27, and the respective inverters 13a, 13b output the AC voltage having the phase difference of 30 degrees, and the operation similar to the conventional one can be performed.

At time t ₁ , when a momentary power failure or a minor failure occurs and a stop command is output, the switch RUN is turned off and the closed loop of the PLL circuit 24 is formed, so that the rotational speed of the AC motor 15 becomes the same as in the conventional case. Following the frequency command f ^* Changes. Further, the external command * RUN is input by the stop command, and the hold circuit 29 receives the voltage reference V ^* at that time ^. Hold.

When the operation of the inverter is stopped by the stop command, the frequency f (rotational speed) becomes equal to the load and GD ^{2 as} shown in FIG. 2 (A). The motor voltage V drops at a faster decay rate because the exciting magnetic flux weakens.

During this period, the divider 25 calculates the voltage ratio K = V / V _dc between the motor voltage V and the DC voltage V _dc . (Note that
Each of V and V _dc is detected as a percentage of the rated voltage, and when operating at the rated value, K = 1 and the output of the function unit 26 becomes zero. ) Therefore, when the inverter stops, the voltage ratio K becomes smaller than 1 and the function unit 26 outputs φ ₁ = cos ^-1.
The K signal φ ₁ is output.

When restarting the operation of the inverter at time t ₂ , the external command s ₁ is given for a predetermined time at the same time as the operation command. In response to this external command s ₁ , the output unit 30 outputs a signal φ ₂ which has the maximum value of the signal φ ₁ at that time and attenuates to zero in a predetermined time, and the pulse distribution circuit 27 outputs the signals from the inverters 13a and 13b. The phase of AC voltage is normal 30
In addition to the output, the output is controlled to be shifted by φ ₂ (= cos ⁻¹ K) degrees. As a result, the voltage vectors V _a and V _b on the secondary side of the transformers 14a and 14b are shifted by ± φ ₂ degrees with respect to the central phase during normal operation as shown in FIG. The secondary voltage V is constant at the center phase and only the magnitude thereof changes according to φ ₂ . Further, the change rate limiting circuit 28 receives the frequency command f ^* by the external command s ₁ ^. Hold temporarily.

On the other hand, when the external command * RUN is turned off by the operation command, the hold circuit 29 is released from the holding state and returned to the function as a mere buffer. At this time, the hold circuit 29 does not do so immediately but functions after a predetermined time. The voltage is gradually decreased so as to reach the voltage reference output from the device 18. Therefore, the DC voltage V _dc gradually decreases from time t _{2 as} shown in FIG. 2A, and the frequency command f ^* held at time t ₃ is held ^. Reaches the value corresponding to. During this time, the signal φ ₂ from the output unit 30 also gradually decreases, and the vector-combined secondary voltage increases even if the DC voltage decreases. When the external command s ₁ is turned off at time t ₃ after the elapse of a predetermined time, the signal φ ₂ of the output section 30 becomes zero, the hold of the change rate limiting circuit 28 is released, and it functions as a normal change rate limiting circuit. Therefore, the frequency command f ^* Is time t
_The frequency is returned from ₃ to the set frequency at the normal rate of change, and the original operating state is restored at time t ₄ . According to this embodiment, the present invention can be easily implemented by symmetrically controlling the phase difference between the AC voltages of the two inverters.

Further, the same operation can be performed by using an 18-pulse inverter using three inverters, and even when three or more inverters are used, each inverter is used.
Similarly, the phase can be controlled by appropriately controlling the phase of the AC voltage.

[0022]

According to the present invention, when the operation of the inverter is temporarily stopped for a short time due to a momentary power failure or a minor failure, and then the operation of the inverter is restarted, the alternating current output from each inverter is output. By controlling the phase of the voltage, it is possible to match the DC voltage and the motor voltage without causing an overcurrent, and to provide a multiplexed voltage source inverter that can be safely and smoothly restarted. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a multiplexed voltage source inverter according to the present invention.

FIG. 2 is a diagram for explaining the operation of the above embodiment,
(A) is a time chart when the inverter restarts.
(B) is a vector diagram of the AC voltage output by the two inverters generated on the secondary side of the transformers 14a, 14b.

3A and 3B are diagrams for explaining a conventional multiplex voltage source inverter, FIG. 3A is a configuration diagram thereof, and FIG. 3B is a time chart for explaining the problem.

[Explanation of symbols]

10 ... Converter 11 ... Reactor 12 ... Capacitor 13a, 13b ... Inverter 14a, 14b ... Transformer 15 ... AC motor 16 ... Frequency setter 18 ... Function unit (V / F) 19 ... Voltage controller 20 ... Voltage Detector 21 ... Integrator 23 ... (AC) voltage detector 24 ... PLL circuit 25 ... Divider 26 ... Function unit (cos- ¹ ) 27 ... Pulse distribution circuit 28 ... Change rate limiting circuit 29 ... Hold circuit 30 ... Output section

Claims (1)

[Claims] 1. A control power supply for outputting a DC voltage according to a voltage command, and a plurality of inverters for converting the DC voltage into AC voltages having different phases, and combining the AC voltages having different phases. In a multiplexed voltage source inverter for driving an AC motor with a voltage, means for controlling the phase of each AC voltage of the plurality of inverters according to the voltage ratio between the DC voltage and the voltage of the AC motor is provided. When the operation of the inverter is stopped due to an abnormal situation, the voltage command is held and the frequency command is changed following the rotation speed of the AC motor to restart the operation of the inverter. Controls the phases of the AC voltages of the plurality of inverters according to the voltage ratio, holds the frequency command, and sets the voltage command and the control phase in a normal operating state for a predetermined time. And a means for returning the frequency command to the normal operating state and then returning to the set frequency, the multiplexed voltage type inverter.