JPH0799959B2 - Inverter with winding switching function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction motor inverter that is required to have a wide constant output control range, such as a spindle drive of a machine tool or a drive of an electric vehicle.

[Conventional technology]

When an induction motor is driven by an inverter, as shown in Fig. 5, the motor terminal voltage is V, the primary frequency is F, and V
If the / F constant control is performed, the constant torque characteristic is obtained, that is, the output is proportional to the rotation speed, except in the low speed range where the voltage drop due to the resistance of the winding or the like cannot be ignored.

If V = constant, a constant output characteristic can be obtained between the lower limit of the operating frequency determined by the motor allowable magnetic flux density and the upper limit of the operating frequency determined by the maximum torque of the motor.

In FIG. 5, the switching points between the constant torque characteristic and the constant output characteristic are shown.
N _B, when the maximum speed in the constant power control and N _M, the induction motor, the ratio N _M / N _B is about 2-3.

Therefore, in order to expand the constant output control range,
N _B may be lowered to N _B1 as indicated by the characteristic b indicated by the alternate long and short dash line in the figure. At this time, the constant output control range is expanded to N _B / N _B1 times, while the rated output is decreased to N _B1 / N _B times, so to expand the constant output range with the same rated output, N _B / N _B1
Double the inverter capacity is required.

As another method of expanding the constant output control range, there is a method of utilizing a difference in output characteristics due to a change in connection of motor windings.
In Figure 6, FIG. 7 shows an output characteristic of a circuit connection example in the case of connection. In FIG. 6, 6 is an induction motor (hereinafter simply referred to as a motor) having 6 terminals in which each winding of the three-phase winding is independent, 15 is an inverter, and 13 is a motor 6. A switch such as an electromagnetic contactor for connection, 14 is a switch for connecting the motor 6 to a Δ connection.

The characteristic c shown by the solid line in FIG. 7 is that the switch 13 is closed and the switch 14 is closed.
Open the motor 6 It is the characteristic when connected and operated, and the constant output characteristic is between N _{B2 and} N _B. Next, the characteristic d represented by the alternate long and short dash line is a characteristic when the switch 13 is opened and the switch 14 is closed and the motor 6 is connected by Δ, and the motor 6 is operated, and the constant output characteristic is between N _{B and} N _M. Therefore, by switching and operating the winding connections, N _B2
From to N _M, although a wide constant power control range is obtained, in order to perform circuit switched mechanically, it produces a switching loss time.

[Problems to be solved by the invention]

As described above, there are two possible methods for expanding the constant output control range, but there are the following problems.

(1) When lowering N _B and expanding the constant output control range, N _B /
N _{B 1} times the inverter capacity is required.

(2) When expanding the constant output control range by switching windings,
Lost time occurs due to winding switching.

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above problems and provide a winding switching type inverter without switching loss time.

[Means for solving problems]

In order to achieve this object, the present invention has, in a voltage source inverter, two sets of three-phase bridge circuits each composed of a power semiconductor switching element such as a thyristor and a transistor. Directly connect the negative electrode terminal to the positive electrode terminal and the negative electrode terminal of the DC voltage source, and connect the other three-phase bridge circuit to the positive electrode terminal and the negative electrode terminal of the DC voltage source via a switch such as a power semiconductor element or an electromagnetic contactor. Connected, the winding of each phase of the induction motor is connected between the corresponding phases of each of the three-phase bridge circuits, and Δ connection operation or equivalent to the switching element of each of the three-phase bridge circuits. It is characterized in that means is provided for providing an on / off signal and a PWM control signal for connection operation.

[Action]

In the present invention, two sets of three-phase bridge circuits and two switches are used, without a mechanical winding switching mechanism. The induction motor is operated by switching between connection operation and Δ connection operation.

When performing the connection operation, a switch provided between the three-phase bridge circuits is turned off, a DC voltage is applied only to one of the three-phase bridge circuits, and a switching element of the other three-phase bridge circuit is turned on. One of the three bridge circuits
By controlling the PWM, the induction motor Connected operation can be performed. When the Δ connection operation is performed, the switch between both three-phase bridge circuits is turned on, and the switching element of each three-phase bridge circuit is PWM-controlled. At this time, the winding itself is not Δ-connected, but the current flowing through the winding is equivalently Δ-connected.

In this way, by controlling the on and off of the switch and the switching element, The operation can be switched between the connection operation and the Δ connection operation.

〔Example〕

Hereinafter, the present invention will be specifically described based on the embodiments shown in the drawings.

FIG. 1 is a basic circuit diagram of the inverter of the present invention. In the figure, 1 is a combination of a rectifying circuit and a smoothing capacitor, a DC voltage source such as a storage battery, 2 is a three-phase inverter bridge circuit,
Reference numeral 3 is a three-phase bridge circuit for switching winding connection. The three-phase bridge circuit 2 includes switch groups 21 to 26,
The three-phase bridge circuit 3 also includes switch groups 31 to 36. The power supply lines of these bridge circuits 2 and 3 are connected by busbar switches 4 and 5 for switching winding connection. The windings 61 to 63 of the motor 6 are connected between the corresponding phases of the bridge circuits 2 and 3.

The bridge circuit 2 has the same function as that of a known PWM control inverter, and by a PWM (pulse width modulation) signal which is a control output signal of V / F control or vector control, as shown in the time chart of FIG. , Switches 21 to 26 are repeatedly turned on and off to generate a three-phase AC voltage. At this time, switch
21 and 24, 22 and 25, and 23 and 26 are set so as to perform an inversion operation to each other and are not turned on at the same time.

On the other hand, the switching of the motor winding connection is performed by the bridge circuit 3 and the switches 4 and 5. Here, the terminals on the bridge circuit 2 side of the windings 61 to 63 are U, V, W, and the terminals on the bridge circuit 3 side are X, Y, Z.

If all the switches 31 to 36 of the bridge circuit 3 are turned on and the switches 4 and 5 are turned off, the terminals X, Y and Z have the same potential,
Moreover, since the positive terminal and the negative terminal of the DC voltage source 1 are electrically disconnected, the motor 6 is Become a connection. In the case of Δ connection, the switches 4 and 5 are turned on, and the switches 31 to 36 of the bridge circuit 3 are turned on and off by the PWM signal. I.e. switches 21 and 33, 22 and 31, 23 and 3
2, 24 and 36, 25 and 34, 26 and 35 are turned on and off with the same PWM signal. As a result, the terminals U and Z, V and X, W of the windings 61 to 63 are
And Y become the same potential, and the motor 6 becomes equivalent to the Δ connection.
Figure 3 shows The potentials of the terminals U, V, W, X, Y, and Z in the case of connection and in the case of Δ connection with respect to the negative terminal of the DC voltage source 1 are shown.

Next, a specific circuit example is shown in FIG. Bridge circuit 2,
The switches 3, 4 and 5 use transistors and diodes connected in anti-parallel. 7 is a base amplifier of a switch transistor of the bridge circuit 2, 8
Is a base transistor amplifier of the switch of the bridge circuit 3, 9 is a base amplifier of the transistors of the switches 4 and 5, and these base amplifiers 7 to 9 have a function of electrically insulating a signal by using a photo coupler or the like. To have. 10 is A switch for selecting connection or Δ connection, 11 is a signal inverting circuit of a logic circuit for inverting a signal, and 12 is an OR circuit for selecting a signal.

The switch 10 is the power source for the signal inverting circuit 11 and the OR circuit 12.
When connected to Vcc, all the transistors of bridge circuit 3 are turned on, the transistors of switches 4 and 5 are turned off,
The windings 61 to 63 of the motor 6 are Become a connection.

When the switch 10 is connected to Vss which is the signal ground of the signal inverting circuit 11 and the OR circuit 12, the transistors of the switches 4 and 5 are turned on, and the transistor of the bridge circuit 3 is the PWM signal connected as shown in FIG. Being driven, it is equivalent to a delta connection.

As described above, the known inverter including the DC voltage source 1, the bridge circuit 2 and the base amplifier 7 thereof is connected to the bridge circuit 3, the switches 4 and 5, the base amplifiers 8 and 9 thereof, and the switches thereof.
By adding a signal selection circuit consisting of 10, signal inversion circuit 11, and OR circuit 12, without a mechanical circuit switching mechanism,
The motor 6 It becomes possible to operate with connection and Δ connection.

Although this embodiment uses a transistor and a diode for the switch, it can also be realized by using a GTO (gate turn-off thyristor) or a thyristor. The control method can be applied to both V / F control and vector control, but it is necessary to change the V / F characteristic accompanying the switching of the winding of the motor 6 and the motor control constant during vector control. .

〔The invention's effect〕

As described above, according to the present invention, by providing two sets of three-phase bridge circuits and two switches, there is no need for a mechanical winding switching mechanism. The induction motor can be operated by switching between connection operation and Δ connection operation. Therefore, the constant output control range of the induction motor can be expanded without increasing the inverter capacity and without winding switching loss time. Especially, when it is applied to a machine tool spindle drive or a drive of an electric vehicle, The effect is demonstrated.

[Brief description of drawings]

FIG. 1 is a basic circuit diagram of an inverter of the present invention, FIG. 2 is a time chart of a bridge circuit, FIG. 3 is a voltage waveform diagram of a winding of a motor, and FIG. 4 is a circuit showing a concrete embodiment of the present invention. Fig. 5 is an output characteristic diagram when the motor is operated by an inverter, Fig. 6 is a circuit diagram showing a main circuit connection example of a conventional winding switching system, and Fig. 7 is a diagram when the winding connection method is switched. It is an example of the output characteristic diagram of inverter operation. 1: DC voltage source, 2, 3: Three-phase bridge circuit 4,5: Switch, 6: Motor 21 to 26, 31 to 36: Switch group 61 to 63: Motor winding

Claims (1)

[Claims] 1. A voltage source inverter comprising a thyristor,
There are two sets of three-phase bridge circuits composed of power semiconductor switching elements such as transistors, and the positive and negative terminals of one of the three-phase bridge circuits are directly connected to the positive and negative terminals of the DC voltage source, respectively. The other three-phase bridge circuit is connected to the positive electrode terminal and the negative electrode terminal of the DC voltage source via a switch such as a power semiconductor element or an electromagnetic contactor, and the induction motor is connected between the corresponding phases of the three-phase bridge circuit. Connect the phase windings and operate Δ equivalence or equivalent to the switching elements of each three-phase bridge circuit An inverter with a winding switching function, which is provided with means for giving an on / off signal and a PWM control signal for connection operation.