JP3333851B2 - How to shut off the output of a three-phase voltage source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for controlling the output current of a three-phase voltage-source inverter for controlling a three-phase AC motor. Output of a three-phase voltage-source inverter that reduces the current reduction rate, avoids large current pulsations between the upper and lower current settings due to rapid current changes, and enables stable limiting control of output current About the method.

[0002]

2. Description of the Related Art Output current limiting control of a three-phase voltage-source inverter for driving and controlling a three-phase AC motor in a power running or regenerative state without a three-phase bridge having a switching element for each phase arm element as its DC / AC converter. In the case where the output current of any one of the three phases of the output becomes equal to or higher than the set current limit value, a method of turning off all the switching elements of each phase of the three-phase bridge is a conventional output cutoff. Known as the method.

[0003]

However, according to the conventional three-phase voltage-source inverter output shut-off method for controlling the output current as described above, when the output current of the inverter becomes equal to or more than the set limit current value. Regardless of the current increasing phase, regardless of the phase difference between the inverter output voltage and the load motor back electromotive voltage at the time of the current increasing, all the switching elements of each phase of the three-phase bridge are turned off. In principle, the inverter output current suddenly decreases at a very large time reduction rate, and when the inverter output current falls below the lower limit current set value by this current reduction control, the inverter output current is inverted and the current increase control is performed. The current is restarted. As a result, a large current pulsation of the inverter output current is caused between the upper and lower current setting values. It had become a thing.

[0004] In view of the above, the present invention aims at alleviating the temporal reduction degree of the inverter output current, and avoiding the large current pulsation as described above to enable a stable output current limiting control. The purpose of the present invention is to provide an output shut-off method.

[0005]

In order to achieve the above object, a method for shutting off the output of a three-phase voltage source inverter according to the present invention comprises the following steps: 1) According to claim 1, a three-phase AC motor that is driven at a variable speed. The present invention relates to a method of shutting off the output of a voltage type inverter, wherein an output current of any one of three phases of an output of the inverter, in which a three-phase bridge in which a switching element is an arm element for each phase serves as a DC / AC conversion unit, is used for powering the motor. If the upper arm switching element of this current increasing phase is in the ON state when the current becomes equal to or more than the set current limit value at the time of the control, ON or OFF for each phase switching element of the three-phase bridge with respect to each phase lower arm element. The operation commands are maintained in their command states, and the upper arm elements of each phase are OFF-controlled in all three phases.

According to a second aspect of the present invention, there is provided a method for shutting off the output of a three-phase voltage-source inverter for driving a three-phase AC motor at a variable speed. If the output current of any one of the three phases of the output of the inverter becomes equal to or larger than the limit current set value during the power running control of the motor, if the lower arm switching element of the current increasing phase is in the ON state, , For each phase switching element of the three-phase bridge,
The ON or OFF operation command for each phase upper arm element is maintained in its command state, and the three phase lower arm elements are OFF controlled for all three phases.

[0007] 3) In the above 1) or 2), when the output current of any one of the three phases of the output of the inverter becomes equal to or larger than the set current limit value during the regenerative control of the motor, It is assumed that all the switching elements of each phase of the bridge are OFF-controlled.

[0008] 4) In the 1) or 2), wherein in the motor restart control period after power failure of the power supply momentary power failure occurs during power running control of the electric motor, one of the phases of the output three-phase in the previous SL inverter When the output current of the three-phase bridge becomes equal to or larger than the set current value, the switching elements of all the phases of the three-phase bridge are turned off.

[0009]

In general, when power is supplied from an AC power supply to an inductive load, the temporal change rate of the load current is proportional to the difference voltage between the power supply voltage and the back electromotive force of the load. For example, as shown in the single-phase equivalent circuit diagram of FIG. 4 which forms the basis of various AC rotating machine drive systems, when a voltage V which is an AC power supply voltage is applied to an inductive load having an inductance L, a current I flows through the load. However, a back electromotive voltage E is generated at the load.

The electric quantities such as V, E, and I are vector quantities and are mutually connected by the following equation (1).

[0011]

(Equation 1)

That is, as shown in the equation (1), for each vector quantity, the temporal change rate of the load current I is the power supply voltage V
And the back electromotive voltage E of the load.
On the other hand, when a three-phase AC voltage is applied to the three-phase winding of the AC rotating machine, the three-phase winding generates a rotating magnetic field whose rotation angular velocity is defined by the frequency of the AC voltage. An electrical angle of 1 corresponds to the rotating magnetic field.
The three-phase AC voltage composed of three types of AC voltages having a phase difference of 20 degrees can be combined and converted into a single rotation voltage vector and handled. Similarly, if the three-phase AC voltage is set as the output voltage of the three-phase voltage source inverter, the back electromotive force generated in the three-phase AC motor to which this voltage is applied can also be handled as a single rotation vector. Become.

As described above, in the output current limiting control of the three-phase voltage source inverter for controlling the driving of the three-phase AC motor,
In order to reduce the temporal change rate of the inverter output current and perform stable control avoiding a large current pulsation, the inverter output voltage and the motor back electromotive voltage, each of which is combined and converted into a single rotation vector, are used. In this regard, the vector difference voltage between the two at the start of the inverter output current reduction control should be as small as possible.

According to the present invention, as described above, in order to reduce the temporal current change rate in the current limit control of the inverter output current, the present invention starts the current limit control accompanying an increase in the inverter output current in any one of the three phases. In order to minimize the vector difference voltage between the inverter output voltage and the motor back electromotive voltage at the time, that is, to obtain an inverter output voltage having an optimal vector state according to the vector state of the motor back electromotive voltage, The ON / OFF control is performed on the switching element of each phase arm of the three-phase bridge that forms the DC / AC converter.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1, 2 and 3 are circuit diagrams of the inverter output unit, and FIGS. 5 and 8 are vector diagrams showing the position change pattern of the rotation voltage vector synthesized and converted from the inverter three-phase output voltage. 6, 7, 9, and 10 are vector diagrams showing a calculation state of a vector difference voltage between the inverter output voltage and the motor back electromotive voltage, which is a rotation vector.

First, referring to FIG. 2 and FIG. 5 corresponding thereto, the basic relation between the ON / OFF state of each phase switching element of the three-phase bridge forming the inverter output section and the position of the rotation voltage vector will be described. Explain the matter. FIG. 2 shows the output of the inverter, that is, its DC /
3 shows a circuit configuration of a three-phase bridge that forms an AC conversion unit and an ON or OFF state in a normal state before starting current limit control with an increase in inverter output current for each phase switching element.

[0017] In FIG. 2, the three-phase bridge is obtained by bridging a transistor having a commutation diode as a switching element of each phase arm, receives the power supply voltage E _d from the DC power supply, U, V, W Output currents I _U, I _{V, and} I _W , respectively. Note that each of the switching elements is a U, V, W
ON / OFF control is performed such that each phase output voltage from each output terminal has a phase difference of 120 electrical degrees and is sequentially and repeatedly output in a predetermined cycle.

The output voltage of each phase of the inverter is expressed as a unit with the power supply voltage _Ed as 1, and the output voltages of the U, V,
W is shown below each output terminal. For example, when the output voltage of the U-phase output terminal is 1 and the output voltages of the V and W output terminals are 0, the U-phase upper arm element of the three-phase bridge is in the ON state, A state in which the positive bus voltage of the DC power supply whose level is 1 is directly output to the U-phase terminal, and a state where the lower arm element of both the V and W phases is in the ON state and whose voltage level is 0, the negative electrode of the DC power supply This shows a state where the bus and the V and W both-phase output terminals are at the same voltage level. Therefore, the currents I _{U, IV and} I _W flow in and out of the U, V and W output terminals in the direction of the arrows through the three-phase windings of the load AC motor, respectively. Maximum in each phase.

FIG. 5 shows a rotational voltage vector obtained by synthesizing and converting the three-phase output voltages of the inverter, and shows ON or OFF of each phase switching element of the three-phase bridge.
It is a vector diagram which shows the positional relationship which changes according to a state. Here, the rotation voltage vector depends on the ON or OFF state of each phase switching element of the three-phase bridge as described in Chapter 6 of "Semiconductor Power Conversion Circuit" published by the Institute of Electrical Engineers of Japan, and therefore, the output voltage of each phase output terminal. It is defined as an instantaneous space voltage vector of the inverter defined by a predetermined functional relationship according to the state, and details of the combined conversion are omitted here, but each voltage vector V _k (k = 0 to 7) as a function of the respective U, V, the output voltage of the W, which is the unit displays the voltage E _d as 1, comprising as formula group (2) below.

[0020]

(Equation 2)

FIG. 5 is a vector diagram in a powering control state of the three-phase AC motor by the three-phase inverter.
Each of the illustrated load current vector I and the back electromotive voltage vector E of the load motor is obtained by synthesizing the three-phase component as a single rotation vector, as in the case of the instantaneous space voltage vector. _This is shown as an example at the time corresponding to ₁ . Temporal change rate of the load current I by the illustrated the voltages V ₁ of a (V ₁ -E) / L according to equation (1), the differential voltage vector (V ₁
−E) and the direction of the voltage vector V _{1 of} both the current vector I, that is, the U-phase component, are in the same direction, indicating that the current is increasing.

Next, FIG. 1 shows a first embodiment of the present invention corresponding to claim 1. That is, each phase switching element of the three-phase bridge is turned on or off as shown in FIG.
According to claim 1, the U-phase upper arm element in the ON state is turned off by turning off the U-phase upper arm element in the ON state, so that the U, V, Turn off all upper arm elements of each W phase,
On the other hand, the lower arm element of each phase maintains the state shown in FIG. Therefore, in FIG. 1, only the U-phase upper arm element is ON as shown in the underline in FIG.
From OFF to OFF.

When the state changes from FIG. 2 to FIG. 1, the U-phase output current I _U flows through the commutation diode of the in-phase lower arm element since the U-phase upper arm element is turned off. The phase output currents I _U, I _V, I _W return to the load motor while maintaining the directions of the arrows shown in FIG. Therefore, the output voltage of the U-phase output terminal changes from 1 to 0 in unit display, and the voltage vector V _k defined by the expression group (2) becomes V (0,0,0), that is, V ₀ . U in this case
The temporal change rate of the phase output current is (V ₀ −E) / L, that is, −E / L in the vector amount according to the equation (1). This state is shown in FIG.

FIG. 3 shows a case according to the conventional method. For example, when the U-phase current becomes equal to or more than the limit current set value,
All the switching elements of each phase of the three-phase bridge are OF
F shows the case. At this time, the U-phase output current I _U passes through the commutation diode of the U-phase lower arm element, and the V and W two-phase output currents I _{V and} I _W are the commutation of the V-phase and W-phase upper arm elements, respectively. The current flows back to the load motor via the diode while maintaining the direction of the arrow shown in FIG.

Therefore, the output voltage of each phase is expressed in units as
U phase goes from 1 to 0, V phase goes from 0 to 1, W phase goes from 0 to 1
Respectively, and the voltage vector V _k becomes V (0, 1, 1).
, That is, V _4. In this case, the temporal change rate of the U-phase output current is (V ₄ −E) / L. This state is shown in FIG. Here, FIGS. 6 and 7 are compared, and the vector E / L is smaller than (V ₄ −E) / L in the size. That is, in the above-described temporal current change rate, the method of the present invention shown in FIG. 6 is significantly smaller than the conventional method shown in FIG. 7, and thus the current pulsation in the output current limiting control is also greatly reduced. Will be done. Note that the -E
Both the U-phase component of the / L and (V ₄ -E) / L vectors are in the opposite direction to the U-phase component of the load current vector I, and therefore the U-phase output current in both FIGS. It is in.

Next, both vector diagrams of FIG. 8 and FIG. 9 are for explaining the second embodiment of the present invention corresponding to claim 3 for regenerative control of the load AC motor.
The ON or OFF state of each phase switching element of the three-phase bridge is the same as in FIG. At the time of the regenerative control of the motor, the motor back electromotive voltage vector E is inverted in that direction as shown in FIG. 8 as compared with the case of FIG. Therefore, in the regenerative control, for example, when the U-phase current becomes equal to or more than the set current limit value, and all the switching elements of the U, V, and W phases of the three-phase bridge are turned off according to claim 3, the voltage vector V _k is V (0,1,
1), that is, V _4.

Therefore, the temporal change rate of the U-phase current is a vector (V ₄ -E) / L as shown in FIG. 8, the U-phase component is in the opposite direction to the U-phase component of the load current vector I, and the U-phase output The current will be in a decreasing state. Here, (V
The value of _4- E) / L is smaller than the temporal current change rate in the powering state shown in FIG. 1, and the current pulsation in the output current limiting control is also smaller.

FIG. 10 shows a case in which the control according to claim 1 is performed during the motor regeneration control, and the voltage vector V _k becomes V (0,0,0), that is, V ₀ , The temporal change rate of the current is vector -E / L, and the U-phase component is in the same direction as the U-phase component of the load current vector I, so that the U-phase output current is in an increased state and the motor regenerative control at the time of motor regeneration control. The method becomes improper. What
Regarding the judgment of power running or regenerative state of the electric motor
Is generally an inverter without any additional circuitry.
Output current and output voltage detection circuit installed in the device
The determination can be easily made based on both detection signals.

According to a fourth aspect of the present invention, in the motor restart control period after the restoration of the instantaneous power failure generated during the power running control of the load AC motor, a certain time is required until the inverter operation is restarted. Since the operation is performed independently of the output voltage, it is difficult to determine whether the powering control or the regenerative control is performed. Therefore, during the restart control period, as in the case of claim 3, when the output current of any one of the three output phases of the inverter becomes equal to or more than the set current limit value, the three-phase bridge Of each of the phases is turned off.

An embodiment of the present invention corresponding to claim 2 is also the same as that of FIG. 1 by reversing the description of the upper and lower arms to which the respective phase switching elements of the three-phase bridge belong. Since it can be explained, the explanation is omitted here.

[0031]

Effect of the Invention] The present invention, when the current limitation control for increasing the pre-Symbol inverter output current, achieving relaxation time rate of change of the current reduction becomes large between the two current set value of the upper and lower limit current A stable output current limiting control can be easily and inexpensively performed by avoiding pulsation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an inverter output unit showing a first embodiment of the present invention (during power running).

FIG. 2 is a circuit diagram of an inverter output unit showing an element switching state when the inverter output current is normal.

FIG. 3 is a circuit diagram of an inverter output unit showing an element open / closed state when the conventional technology is applied (during power running).

FIG. 4 is a single-phase equivalent circuit diagram of an AC rotating machine drive system

FIG. 5 is a vector diagram of an instantaneous space voltage vector of the inverter (during power running).

FIG. 6 is a vector diagram of a vector difference voltage calculation vector corresponding to FIG. 1 (during power running).

7 is a vector diagram of a vector difference voltage calculation vector corresponding to FIG. 3 (during power running).

FIG. 8 is a vector diagram of an instantaneous space voltage vector of the inverter (at the time of regeneration).

FIG. 9 is a vector diagram showing a vector difference voltage operation vector according to the second embodiment of the present invention (during regeneration);

FIG. 10 is a vector diagram of a vector difference voltage operation vector corresponding to FIG. 1 (at the time of regeneration)

[Explanation of symbols]

E _d DC power supply voltage E Load motor back electromotive voltage (vector) I _U inverter U-phase output current _IV inverter V-phase output current I _W inverter W-phase output current L Inverter load path overall inductance _Vk inverter Instantaneous space voltage vector (k = 0 to
7)

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02H 7/122 H02H 7/08 H02M 7/48 H02M 7/5387

Claims (4)

(57) [Claims] 1. A method for shutting off the output of a three-phase voltage source inverter for driving a three-phase AC motor at a variable speed, wherein the three-phase bridge having a switching element for each phase arm element as a DC / AC converter is provided. If the output current of any one of the three output phases becomes equal to or more than the set current limit during power running control of the motor, if the upper arm switching element of this current increasing phase is in the ON state, For each phase switching element of the phase bridge, the ON or OFF operation command for each phase lower arm element maintains its command state, and for each phase upper arm element, all three phases are OFF.
A method for shutting off output of a three-phase voltage source inverter, characterized by controlling. 2. A method for shutting off output of a three-phase voltage type inverter for driving a three-phase AC motor at a variable speed, wherein the three-phase bridge having switching elements as arm elements as a DC / AC converter is provided. If the output current of any one of the three output phases becomes equal to or greater than the set current limit during power running control of the motor, if the lower arm switching element of this current increasing phase is in the ON state, For each phase switching element of the phase bridge, the ON or OFF operation command for each phase upper arm element maintains its command state, and for each phase lower arm element, all three phases are OFF.
A method for shutting off output of a three-phase voltage source inverter, characterized by controlling. 3. A method according to claim 1 , wherein the output current of any one of the three phases of the output of the inverter is set to a limited current value during a regenerative control of the motor. In the above case, a method of shutting off the output of the three-phase voltage-source inverter, characterized in that all the switching elements of each phase of the three-phase bridge are turned off. 4. The method of claim 1 or 2 three-phase voltage-type output cutoff method inverter, wherein in the motor restart control period after power failure of the motor power supply momentary power failure occurring during power running control of the pre-Symbol inverter A three-phase voltage source that turns off all the switching elements of each phase of the three-phase bridge when the output current of any one of the three output phases becomes equal to or more than the set current limit value. Inverter output shutoff method.