JPH03265484A - Control method for voltage type inverter - Google Patents

Abstract

PURPOSE:To obtain a large torque under low speed without increasing the capacity of an inverter by arranging power modules at a converter section and an inverter section alternately on a heat sink. CONSTITUTION:Since the allowable capacity of a heat sink 6 is fixed, approximately same amount of loss is produced at a converter section 1 and an inverter section 2 under high speed at the time of spindle driving, for example, and thereby only a rated torque is produced. In case of low speed operation at the time of C shaft driving, for example, load at the converter section 1 is low and thereby loss is reduced at the converter section. Consequently, allowable loss for the power modules 21-26 at the inverter section 2 distributed on the heat sink 6 increases to allow for a large loss, and thereby a torque larger than the rating torque can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage source inverter having a power regeneration function.

[Prior Art] Conventionally, many PWM-controlled voltage source inverters that have a power regeneration capability using a transistor converter or the like are used when performing high-frequency acceleration/deceleration operations, such as in the main shaft drive of a machine tool.

Figure 4 shows the circuit configuration of a voltage source inverter with a transistor converter. 1 is a converter consisting of six sets of transistors and diodes connected in antiparallel, 2 is an inverter also consisting of six sets, and 3 is a converter consisting of six sets of transistors and diodes connected in antiparallel. It is a smoothing capacitor.

In such an inverter device, a power module shown in FIG. 5 is constituted by these anti-parallel connected transistors and diodes, and is attached to a heat sink for cooling. FIG. 6 shows the structure of the main circuit section of a conventional inverter device.

Reference numeral 6 denotes a heat sink to which power modules and the like are attached.The converter 1 is composed of six power modules 11-16 having the structure shown in FIG. 5, and the inverter 2 is composed of power modules 21-26 having the same structure. 4 is a bus bar on the positive voltage side, and power modules ii to 13.
21 to 23 are connected to the positive side terminals of the capacitor 3, 5 is a negative voltage side bus bar, and power modules 14 to 16.
24 to 26 and the negative terminal of the capacitor 3 are connected.

Furthermore, Japanese Patent Application Laid-Open No. 1-278058 discloses that in a circuit in which a plurality of antiparallel first and second semiconductor elements are connected in series, the first and second semiconductors are alternately stacked via a cooling member. Accordingly, a method is disclosed in which the distribution of heat load is equalized.

[Problem to be solved by the invention] In the case of a spindle drive for a machine tool that has a direct spindle indexing position control (hereinafter referred to as C-axis drive) function, a high speed and rated torque are required when driving the spindle, and when driving the C-axis, the rated torque is required. A large torque exceeding the rated value is required at low speed. However, in the conventional power module arrangement shown in Figure 6, in which the power modules for the inverter section and the converter section are arranged separately in their own groups, if the capacity is selected as the main shaft drive, the converter section will be activated during C-axis control. Although the load is light, the inverter section becomes overloaded, causing a local temperature rise and causing element destruction. Therefore, in order to prevent overloading of the inverter section, it was necessary to select an inverter with a larger capacity.

Furthermore, in the device disclosed in Japanese Patent Application Laid-Open No. 1-278058, first and second semiconductor elements having different load conditions in terms of time are arranged alternately to reduce the size of the cooling member. Since the torque is maximized regardless of the speed, it is not possible to obtain large torque beyond the rated value at low speeds.

Therefore, an object of the present invention is to obtain large torque at low speeds without increasing the inverter capacity.

[Means for Solving the Problems] The present invention provides a voltage source inverter capable of power regeneration, which has a three-phase bridge-connected inverter section and a converter section having the same circuit configuration as the inverter section. A power module consisting of a transistor or the like is used as the main circuit element of the converter section and a power module of the inverter section are arranged alternately on a heat sink for cooling the main circuit element,
During low-speed operation, the current limit value of the inverter section is increased as the speed decreases.

[Function] The power modules of the converter section and the power modules of the inverter section are arranged alternately on the heat sink so that the maximum total loss generated by the power modules on the heat sink is constant during both high-speed operation and low-speed operation. During low-speed operation, the current limit value of the inverter section is set to increase as the speed decreases, so the same inverter can generate a rated torque at high speeds and a torque greater than the rated torque at low speeds.

[Example] The present invention will be described with reference to embodiments shown in the drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention, in which reference numerals 11 to 16 are power modules of the converter section 1, which are the same as those shown in FIG. power modules and power modules of the inverter section 2 are alternately arranged on the heat sink 6. 3 is a capacitor; 4 is a bus bar 5 on the positive voltage side; and 4 is a bus bar on the negative voltage side.

When arranging power modules like this, the allowable heat sink loss is determined, so at high speeds such as when driving the main shaft, converter section 1 and inverter section 2 generate the same amount of loss, so only the rated torque can be obtained. However, when operating at a low speed like a C-axis drive, the load on the converter section 1 is small, so the loss generated in the converter section is reduced, so the power module of the inverter section 2 distributed on the heat sink 6 Since the allowable generated loss for 21 to 26 increases and the generated loss can be increased, a large torque exceeding the rated value can be obtained.

In addition, in the constant torque control region during C-axis drive, the maximum load on the converter section 1 is proportional to the speed, so in order to make maximum use of the cooling capacity of the heat sink 6, it is necessary to change the torque limit level as a function of the speed. good.

Fig. 2 shows a control block diagram of the inverter device.
2 is a converter section, 2 is an inverter section, 31 is a speed controller, 32 is a torque limiter, 33 is a torque controller, 34 is a current controller, 35 is a DCCT for output current detection (
36 is a motor, and 37 is an encoder for detecting the motor speed.

The motor 36 is controlled so that the actual speed detected by the encoder 37 matches the speed command.

That is, the speed controller 31 inputs a speed command and a speed detection signal, and outputs a necessary torque command.

The torque limiter 32 prevents this torque command from becoming excessive.
This is to limit the amount to a level that does not cause damage to the device. The output of this torque limiter 32 is transferred to a torque controller 33.
input and converts it to a motor current command. Current controller 3
4. The inverter section 2 and the DCCT 35 constitute a current control loop, and supply a current to the motor 36 to generate torque.

Here, since the maximum value of the motor current can be limited by the torque limiter 32, the maximum loss generated in the power modules 21 to 26 of the inverter section 2 can also be limited.

That is, in the constant torque control region, the generated loss in the power modules 11 to 16 of the converter section 1 is almost proportional to the speed, so the torque limit level is changed as a function of the speed to keep the maximum total generated loss on the heat sink constant. be able to.

Therefore, in the past, the torque limit level was not related to the rotational speed (set constant), but in the present invention, as shown in FIG. 3, by making the torque limit level a function of speed, the cooling capacity of the heat sink is increased. The torque of the inverter section 2 can be further increased by making full use of the torque.

As described above, by changing the arrangement of the power module on the heat sink and making the torque limit level variable as a function of speed, it is possible to obtain the characteristics of a main shaft drive and a C-axis drive with a single inverter. I can do it.

Although the present embodiment describes a main shaft drive of a machine tool, the main circuit power module can be arranged and controlled in the same way for any inverter that has a transistor converter and is controlled with constant torque.

[Effects of the Invention] As described above, according to the present invention, even if the same power module and heat sink as before are used, the motor torque can be increased when the load on the converter section is light, such as at low speeds, and the motor torque can be increased at high speeds. The present invention has the effect of providing an inverter that is capable of generating rated torque at high speeds and large torque exceeding the rated value at low speeds with the same inverter that is capable of generating rated torque at high speeds and large torque exceeding the rated torque at low speeds. .

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 is a block diagram of the invention, Fig. 3 is an explanatory diagram explaining the characteristics of a torque limiter, and Fig. 4 is a diagram of a voltage source inverter with a transistor converter. FIG. 5 is a circuit diagram of a power module in which transistors and diodes are connected in antiparallel, and FIG. 6 is a perspective view showing a conventional method of arranging a power module on a heat sink. 1...Converter section, 2...Inverter section, 3...
- Capacitor, 11-16... Power module of converter section, 21-26... Power module of inverter section, 31... Speed controller, 32... Torque limiter, 33... Torque controller , 34... Current controller, 35... DCCT, 36... Motor, 37...
・Encoder 1 Figure Figure Figure Figure

Claims (1)

[Scope of Claims] 1. In a voltage source inverter capable of power regeneration, which has a three-phase bridge-connected inverter section and a converter section having the same circuit configuration as the inverter section, the main circuit elements of the voltage source inverter include transistors. diodes, the power modules of the converter section and the power modules of the inverter section are arranged alternately on a heat sink for cooling the main circuit elements, and the current of the inverter section is reduced during low-speed operation. A method for controlling a voltage source inverter, characterized in that a limit value is increased as the speed decreases.