JPS61293196A - Inverter circuit - Google Patents

Abstract

PURPOSE:To suppress the increase in the switching loss of a main semiconductor switch due to a reverse recovery current by connecting the second semiconductor switch which switches at a high speed in a anti-parallel with the main switch. CONSTITUTION:In one phase of an inverter, i.e., upper and lower arms, the upper arm is formed of a main semiconductor switch 24 and the second semiconductor switch 26 connected in anti-parallel with the switch 24, and the lower arm is formed of a main semiconductor switch 25 and the second semiconductor switch 27 connected in anti-parallel with the switch 25. When the switch 24 of the upper arm is closed, a load current IL flows from a DC power source side to the load. When the switch 24 is opened, the second switch 27 of the lower arm of the opposed arm is simultaneously closed. Thus, the load current IL communicates to the switch 27, thereby becoming so-called flywheeling mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a voltage type inverter circuit that converts alternating current into a 1a current.

[Prior art and its problems]

FIG. 3 is a main circuit connection diagram showing a conventional example of a voltage source inverter, in which DC power obtained from an AC power source 1 and a rectifier 2 is applied to a transistor inverter via a smoothing capacitor 3 to convert it into AC power. This AC power is used to drive the induction motor 8 at a desired speed. t″
The upper and lower arms are composed of a transistor 4 as a main semiconductor switch, a diode 6 connected in anti-parallel to it, and a transistor 5 as a main semiconductor switch and a diode 7 connected in anti-parallel to it. If you collect the required number of upper and lower arms, for example 3 sets, you will get a 3-phase transistor inverter.This inverter is an induction motor.
When driving a diode such as 6°7, the electric 1
It has the role of supplying a flywheeling current to a8, and supplying a regenerative current from this motor 8 during braking.Among inverter control methods, pulse width variable control is used to control the alternating current voltage and frequency given to the motor 8 by this inverter section. It is widely used because it can be controlled by

Figure 4 is an operating waveform diagram for one phase when the inverter shown in Figure 3 operates under pulse width modulation control;
A) shows the operating signal of transistor 4, FIG. represents the change in the load current ■L flowing to the load. That is, time 1[+.

At ¥11 below, transistor 4 is on and the load current I
, flows from this transistor 4 through the load to the transistors in the other arms of the inverter.

In this state, when an off signal is applied to the transistor 4 at time 1'1, the load current I starts commutation to the diode 7 forming the opposing arms of the same phase, and this commutation is completed at time T2. The period from time T2 to time T3 is the flywheeling mode, and the load current I is this diode 7.
However, at time T3, the current flows through transistor 4.
When a signal is applied to turn on the transistor 4, the transistor 4 starts supplying a load current, and also causes a reverse 41it current to flow through the diode 7 until time T4 when the diode 7 recovers its reverse blocking ability. Therefore, when the transistor 4 is turned on, the load current IL and the reverse recovery current of the diode 7 superimposed thereon flow, thereby causing a switching loss.

FIG. 5 is a diagram showing temporal changes in the current path of the operating waveform shown in FIG. 4, and FIG.
Figure (B) shows the period from time rl+1 to time T2, Figure 5 (C) shows the time from time T2 to time T3, and Figure 5) shows the time from time T3.
From time T4 to time T4, the current path shown in Figure 5 (the river shows the current path after time T4) is clearly shown in Figure 5. When transistor 4 is on, the load current IL
In other words, the load current 1 when the transistor 4 is off and in the flywheeling mode is the diode current ■7 (see Figure 5 (a) and (e)).・Refer to Figure 5 (C)), but when transistor 4 switches from on to off, Figure 5 (B)
Transistor current I4 and diode current 1 as shown in
1 flows to the load, and when transistor 4 switches from off to on, current flows from transistor 4 and diode 7 to the load as shown in FIG. supplies reverse recovery current to

FIG. 6 is a diagram showing the state of the reverse recovery current flowing through the diode. FIG. 6 (a) shows the direction of the current flowing through the diode 7, and FIG. 6 (b) shows the change in the current flowing through the diode 7. are doing. In other words, if the current flowing through the diode 7 in the forward direction is INF, the value of the reverse recovery current 17B flowing through the diode 7, as shown in FIG. The larger the forward current INF is, the larger the liquid reduction gradient of 7F is, and the larger the forward current INF is. Since the magnitude of INF is approximately determined by the load, the attenuation slope -''/dt depends on the inductance value in the circuit and the switching characteristics when the transistor 4 is turned on.

From the above, in the conventional circuit shown in Figure #I3, the main semiconductor switch (transistor 4 in Figure 3)
．． 5 etc.), when the switching speed is high, the current attenuation gradient -ds/at during diode reverse recovery becomes large, so the reverse recovery current becomes large and the switching loss increases. Otherwise, there is a risk that a loss exceeding the reverse recovery loss withstand capacity of the diode will occur in this diode and cause it to be destroyed.
...□・Figure 7 is a main circuit connection diagram showing another conventional example of a voltage source inverter, and the inverter can be switched at high speed.

This is designed to eliminate the above-mentioned drawbacks that occur when the device is constructed with a chain. That is, AC power supply I and rectifier 2
The inverter that converts the DC power obtained by the and smoothing capacitor 3 into AC power to be applied to the induction motor 8 uses metal oxide semiconductor field effect transistors (hereinafter abbreviated as MOSFETs) 14 and 15 as main semiconductor switches. When high-speed diodes 16 and 17 are connected in antiparallel, it is necessary to provide a reactor 18 between the smoothing capacitor 3 and this inverter to alleviate the current attenuation gradient d i/a t during reverse recovery. I don't get it.

In other words, when using an inverter with high-speed switching operation, a reactor must be inserted into the main circuit in order to prevent damage to the main semiconductor switch and the diodes connected in antiparallel to it. This has the disadvantage that the device becomes large and expensive.

[Purpose of the invention]

An object of the present invention is to provide an inverter circuit that can use a semiconductor switch that can perform high-speed switching without increasing switching loss when the main semiconductor switch is turned on.

[Key points of the invention]

This invention uses a high-speed switch instead of a diode in the main semiconductor switch that performs high-speed switching operation.

By connecting a second semiconductor switch capable of switching operation in antiparallel, the reverse switching operation when commutating the load current is eliminated and an increase in switching loss is suppressed. The increase in switching loss can be suppressed by operating the semiconductor switch in the opposite direction to that of the main semiconductor switch on the opposite arm of the same phase.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of an inverter for one phase based on the present invention.

One phase of the inverter, that is, the upper and lower arms, includes an upper arm formed by a main semiconductor switch U and a second semiconductor switch connected in antiparallel to this, and an upper arm formed by a main semiconductor switch 5 and a second semiconductor switch connected in antiparallel to this. The inverter is configured with a switch γ, and DC power is applied to this inverter from a DC power source 10) via a smoothing capacitor 3. In FIG. 1, the main semiconductor switch 25 and the second semiconductor switch 27 are shown as a combination of a diode and a contact. It corresponds to the direction.

In Fig. 1, when the main semiconductor switch on the upper arm is on, a load current flows from the DC power supply side to the load, but at the same time when the main semiconductor switch on the opposite arm is turned off, By turning on the second semiconductor switch n of the side arm, the load current IL is commutated to the second conductor switch n, resulting in a so-called flywheeling mode. Subsequently, the second semiconductor switch γ is turned off at the same time as the main semiconductor switch is turned on again.

At this time, the flywheeling current that had been flowing through the second semiconductor switch γ is attenuated depending on the characteristics of the second semiconductor switch 27, and the load current IL is commutated to the main semiconductor switch 24. At this time, no current (reverse recovery current in the conventional circuit) flows from the main semiconductor switch to the second semiconductor switch nail.

FIG. 2 is a time chart showing the operation of each semiconductor switch in the embodiment circuit shown in FIG. 1, in which FIG. 2 (a) is the control pulse of the phase shown in FIG. Operation signal of the main semiconductor switch of the upper arm, Fig. 2 (/1
is the second semiconductor switch on the lower arm.

2) is the operating signal of the main semiconductor switch 5 of the lower arm, and FIG. 2 (E) is the operating signal of the main semiconductor switch 5 of the upper arm.
Each of them generates an operation signal for the cow conductor switch 5.

In Fig. 2, in response to the basic control pulse of the relevant phase, the main semiconductor switch 5 of the upper arm and the main semiconductor switch 5 of the lower arm are turned on at the same time to prevent an arm short-circuit accident. The second semiconductor switch n on the lower arm operates in a completely opposite manner to the main semiconductor switch n on the upper arm, and the second semiconductor switch n on the upper arm Since the semiconductor switch % is controlled by the second semiconductor switch driving means so as to operate completely opposite to the main semiconductor switch δ of the lower arm, it is possible to prevent the reverse recovery current from flowing as described above.

〔Effect of the invention〕

According to the present invention, in configuring a voltage source inverter, instead of connecting diodes in antiparallel to the main semiconductor switch, a second conductor switch that performs high-speed switching operation is connected, and the main semiconductor switch is connected to the main semiconductor switch.

If the second conductor switch provided on the opposite arm of the same phase operates completely in the opposite direction to the operation of TE, the increase in switching loss of the main semiconductor switch due to reverse recovery current can be suppressed. Since there is no need to insert the 11 actuator for suppressing reverse recovery current into the main circuit, there is an effect that the inverter can be installed in a smaller size and at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the inverter for one phase based on the present invention, and FIG. 2 is a circuit diagram showing the embodiment circuit shown in FIG.
4 is a time chart showing the operation of each semiconductor switch in FIG. Fig. 3 is a main circuit connection diagram showing a conventional example of a voltage source inverter, Fig. 4 is an operating waveform diagram for one phase when the inverter shown in Fig. 3 is operated with pulse width adjustment control, and Fig. 5
The figure shows the temporal change in the current path of the operating waveform shown in Fig. 4, the figure 6 shows the state of the reverse recovery current flowing through the diode, and the figure 7 shows another conventional example of a voltage source inverter. Main circuit connection diagram showing Ol...AC power supply, 2...
- Rectifier, 3... Smoothing capacitor, 4.5... Transistor, 6.7... Diode, 8... Induction motor, lO... DC power supply, 14, 15... MO8F
E'l', j6.17.19-1"i, t-)', 1
8・I+ 7 ri) A', Figure 1 Figure 2

Claims (1)

[Claims] In an inverter in which main semiconductor switches are connected in series to form upper and lower arms, and the plurality of upper and lower arms are connected to a common DC power source to sequentially operate each of the main semiconductor switches to output AC power, the main semiconductor switches A second semiconductor switch is connected in antiparallel to each of the switches, and an inverted signal of the main semiconductor switch drive signal of one arm of each upper and lower arm is connected to a second semiconductor switch of the other arm of the upper and lower arms.
An inverter circuit comprising second semiconductor switch driving means for applying a driving signal to the semiconductor switch.