JPH0488884A - Voltage type inverter - Google Patents

Abstract

PURPOSE:To approach an input current waveform to a sine wave, to reduce the capacity of an AC input side filter and to reduce in size a device by PWM- controlling an inverter module, and composing a converter module of a bidirectional switching element. CONSTITUTION:A bidirectional switching element 301 of a converter module 3 is PWM-controlled by a PWM signal. Simultaneously, an inverter module 4 is PWM-controlled to reduce the capacity of an AC filter made of a reactor 1 and a capacitor 2.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a voltage source inverter, and more specifically, the present invention relates to a voltage source inverter, which includes a filter on the AC input side, a converter module, and an inverter module, does not have a smoothing capacitor in the DC intermediate circuit, and , relates to a voltage source inverter in which each of the modules described above is PWM controlled.

(Prior Art) FIG. 5 shows the main circuit configuration of a first conventional example of this type of voltage source inverter. That is, this voltage source inverter includes a converter module 3A to which a filter reactor 1 and a filter capacitor 2 are connected to the AC input side, and an inverter module 4 connected to the DC output side (DC intermediate circuit). Each module 3A,
The reversible operation of No. 4 enables power and regeneration operations. Here, each module 3A, 4 is configured by connecting six unidirectional switching elements such as power transistors with anti-parallel diodes in a three-phase bridge connection.

In the same figure, R, S, T are AC output terminals on the power supply side, R, S, T are AC input terminals of the converter module 3A, P, N are DC intermediate terminals, and IM is an induction motor as a load. It shows.

Next, FIG. 6 shows the main circuit configuration of a second conventional example.

The mutual connection configuration of the filter reactor 1, filter capacitor 2, converter module 3B, and inverter module 4 in this conventional example is the same as that shown in FIG. connected and configured.

(Problem to be Solved by the Invention) In the voltage source inverter shown in FIG. 5, the portion to the right from the DC intermediate terminals P and N acts as a current source due to the influence of the leakage inductance of the induction motor IM, and is similar to a current source inverter. It has characteristics. On the other hand, since the converter module 3A is originally a converter module for a voltage source inverter, the AC input terminals R,, S, .
The input current to T cannot be made close to a sine wave. For this reason, if an attempt is made to make the inflow current from the AC power supply approach a sine wave, the filter capacity on the AC input side increases, resulting in an increase in the size and cost of the device.

On the other hand, in the voltage source inverter shown in FIG. 6, instantaneous space voltage vector control is performed in the inverter module 4, and by generating a zero voltage vector of 2 or V and putting the inverter module 4 into freewheeling mode,
The current in the DC intermediate circuit is reduced to zero, and the converter module 3
Thyristor B is turned off. This method of control is
This is performed based on online prediction of the motor stator current vector and the power supply side capacitor voltage vector, which has the disadvantage that the control method is complicated and expensive.

The first invention was made to solve the above problems, and its purpose is to use a bidirectional switching element in the converter module, and to convert the PWM signal to the switching element into a trapezoidal modulated wave and a triangular modulated wave. By generating the waveform by comparison with a wavy carrier wave, the input current waveform of the converter module is brought closer to a sine wave, and the capacitance of the AC input side filter is reduced, making it possible to downsize the device and simplifying the control method. An object of the present invention is to provide a voltage source inverter that enables cost reduction.

In addition to the configuration of the first invention, the second invention also provides a method for reducing wiring inductance by connecting a filter capacitor directly or very close to the AC input terminal in the converter module. Reduce costs by reducing the capacity or omitting snubber capacitors.

The purpose of this invention is to provide a voltage source inverter that allows the device to be miniaturized.

(Means for Solving the Problems) In order to achieve the above object, a first invention provides a converter module including a filter connected to an AC input side and a bridge-connected switching element; In a voltage source inverter comprising an inverter module connected to the DC output side without a smoothing capacitor, the inverter module is PWM controlled, and the linear converter module is constituted by a bidirectional switching element,
The converter module is subjected to PWM control using pulses generated by comparing a trapezoidal modulated wave and a triangular carrier wave.

Further, it is preferable that the converter module is controlled so as not to resonate with the filter, and that the number of pulses for PWM control of the converter module is 17 per half cycle of the AC power supply voltage.

Furthermore, in addition to the configuration of the first invention, the second invention is one in which a filter capacitor is connected directly or very close to the AC input terminal in the converter module.

(Function) According to the first invention, since the converter module is configured with bidirectional switching elements, it is possible to operate the lever current source inverter as a converter. Also,
By controlling this converter module using a PWM signal generated by comparing a trapezoidal modulated wave and a triangular carrier wave, the input current waveform to the converter module can be made close to a sine wave, and the AC input side Filter capacity can be reduced.

Furthermore, according to the second invention, by connecting the filter capacitor directly or very close to the AC input terminal in the converter module, the wiring inductance due to the actual wiring part is reduced, and the switching of the switching elements constituting each module is reduced. The spike voltage associated with this decreases. This allows the switching element to have a relatively low breakdown voltage, and the snubber circuit to have a small capacity.

(Example) The present invention will be described in detail below with reference to the drawings.

First, FIG. 1 shows an embodiment of the voltage source inverter according to the first invention, and in the same figure, 1 is a filter reactor, 2 is a filter capacitor, and 4 is a filter reactor.
is a PWM-controlled inverter module configured by connecting six power transistors with anti-parallel diodes in a three-phase bridge connection, and IM is an induction motor. Reference numeral 3 denotes a PWM-controlled converter module, and this converter module 3 is constructed by connecting six bidirectional switching elements, three inches, in a three-phase bridge. In addition, in FIG. 1, the DC intermediate circuit between the converter module 3 and the inverter module 4 has a structure that does not include a smoothing capacitor.

FIG. 2 shows an example of the bidirectional switching element 301, which is composed of a diode bridge 302 and a power transistor 303 as a self-extinguishing element.

Note that FIG. 3 shows the base signal (PWM signal) waveform for the power transistor 303, and a PWM control circuit (not shown) compares the trapezoidal modulation wave e@ and the triangular carrier wave ec, and em A base signal is generated that becomes logic “1” when ≧ec and becomes logic “0” when e■ (ec), and this base signal is applied to power transistors 303 of the upper and lower arms of converter module 3.
can be added by inverting the logic of each other.

As a result of repeated simulations, various studies, and experiments regarding the main circuit configured as shown in FIG. 1, the inventors have obtained the following knowledge. That is, (1) When the frequency of the harmonics of the current flowing through the AC power supply matches the resonant frequency of the AC filter consisting of the AC input side steering wheel l and capacitor 2, the capacity of the AC filter increases due to this resonance.

(2) By generating the PWM signal of the converter module 3 by comparing the trapezoidal modulation wave e- and the triangular carrier wave ec as shown in FIG. 3, the input current waveform of the converter module 3 can be changed. The capacity of the AC filter can be reduced by making it closer to a sine wave.

(3) When employing the control method described in (2) above, if the number of pulses generated in a half cycle of the AC power supply voltage is set to 17 as shown in FIG. 3, the capacity of the AC filter can be reduced by one level.

Therefore, in the main circuit configuration shown in FIG. 1, by performing PWM control on the bidirectional switching element 301 of the converter module 3 using the PWM signal shown in FIG. It is possible to reduce the capacity of an AC filter consisting of

Next, FIG. 4 shows the main circuit configuration in an embodiment of the second invention. In this embodiment, the filter capacitor 2 is connected to the AC input terminals R, , of the converter module 3.
S, , T, and other configurations and control methods are the same as in the first invention.

According to this embodiment, by directly connecting the filter capacitor 2 to the AC input terminals R, , S, , T, the wiring inductance can be reduced compared to actual wiring, and the converter module 3 and inverter module 4 The spike voltage that occurs during switching can be reduced. Therefore, it is possible to use a low voltage switching element, reduce the capacity of a snubber capacitor (not shown) or omit it, thereby reducing costs and downsizing the device. Note that the filter capacitor 2 is connected to the AC input terminals R, .
S,, T, Nogo (similar effects can be obtained even if connected nearby).

(Effects of the Invention) As described above, according to the first invention, a bidirectional switching element is used in the converter module, and the converter module is controlled by a PWM signal generated by comparing a predetermined modulated wave and a carrier wave. Since the filter capacity on the AC input side is reduced, it is possible to reduce costs and downsize the device.

Further, according to the second invention, since the filter capacitor is connected directly or very close to the AC input terminal in the converter module, the spike voltage accompanying the switching of the switching elements constituting each module is reduced by reducing the wiring inductance. be able to. Therefore, a switching element with a relatively low breakdown voltage can be used, and the capacity of the snubber circuit can be reduced or the snubber circuit can be omitted, resulting in further cost reduction and miniaturization of the device.

[Brief explanation of drawings]

FIG. 1 is a main circuit configuration diagram of an embodiment of the first invention, FIG. 2 is a diagram showing an example of a bidirectional switching element, and FIG. 3 is a waveform diagram showing the principle of generation of a base signal of a power transistor. Figure 4 is a main circuit configuration diagram of an embodiment of the second invention;
The figure is a main circuit configuration diagram of a first conventional example, and FIG. 6 is a main circuit configuration diagram of a second conventional example. 1... Filter reactor 2... Filter capacitor 3... Converter module 301... Bidirectional switching element 302... Diode bridge 303... Power transistor 4... Inverter module

Claims (4)

[Claims] (1) Consists of a converter module with a filter connected to the AC input side and bridge-connected switching elements, and an inverter module connected to the DC output side of this converter module without using a smoothing capacitor. In the voltage source inverter, the inverter module is PWM controlled, the converter module is configured with bidirectional switching elements, and the converter module is configured to include:
A voltage source inverter characterized in that it is PWM controlled by pulses generated by comparing a trapezoidal modulated wave and a triangular carrier wave. (2) The voltage source inverter according to claim (1), wherein the converter module is controlled so as not to resonate with a filter on the AC input side. (3) The voltage source inverter according to claim (1) or (2), wherein the number of pulses for PWM control of the converter module is 17 per half cycle of the AC power supply voltage. (4) Consisting of a converter module with a filter connected to the AC input side and bridge-connected switching elements, and an inverter module connected to the DC output side of this converter module without using a smoothing capacitor. In the voltage source inverter, the inverter module is PWM controlled, the converter module is configured with bidirectional switching elements, and the converter module is configured to include:
PWM control is performed using pulses generated by comparing a trapezoidal modulated wave and a triangular carrier wave, and a capacitor constituting the filter is connected directly or very close to an AC input terminal in the converter module. A voltage source inverter characterized by: