JPS6231376A - Pwm inverter - Google Patents

Abstract

PURPOSE:To improve the responsiveness of a current by decreasing a carrrier frequency in a range of a small current command to reduce the insensitive band of a current. CONSTITUTION:A triangular carrier signal generator of PWM inverter has a triangular signal generator having a comparator 21, an operational amplifier 22, resistors 27, 28 and a capacitor 29, and a window comparator having comparators 24, 25, an inverter 26 and an analog switch 23 (parallel with a resistor 27) are added thereto. Thus, when a current command Ia falls within a preset range of -DELTAV<Ia<DELTA V, the output of the window comparator becomes a low level and the output of the inverter 26 becomes a high level to turn ON the switch 23, thereby shortcircuiting the resistor 27. Thus, the period of the output (carrier signal) of the amplifier 22 increases (becomes a low frequency), thereby reducing the insensitive band of the current controlled in the pulse width.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a PWM inverter.

[Conventional technology]

AC servo controllers and DC servo controllers generally amplify the deviation between an AC or DC current command and a feedback current using a current amplifier, and perform pulse width modulation on this amplified current deviation using a triangular wave carrier signal.
Converts to the on/off period of the carrier signal. This on/off signal becomes a drive signal for 4 power transistors in the case of DC type fiMII, and 6 in the case of AC current control.
This becomes the drive signal for the power transistors.

Figure 4 is a configuration diagram of a conventional example of an AC current controlled PWM inverter.This conventional example consists of six power transistors ↑r
+ , Trz, Trs, Tra, Trs
.

Trb, diode DI, 02.03. [+4.
US, 06, an inverter power circuit 1 that drives the motor 2, a current amplifier 3 that amplifies the deviation between the current command In and the current detection signal (feedback current) Iufb, and the current Ima and ``irL current detection signals. (feedback current) A current amplifier 4 that amplifies the deviation of Ivrh, a current calculation circuit 5 that generates a current 1w' from the output of the current amplifier 3.4 σM, 1ma0, and a triangular wave carrier signal generator 10
and the output 1 (+', rv
'.

A comparator that compares the voltage of Iw' with the carrier signal 6.
7.8 and the output of the comparator 6.7.8, the power transistors Tr+, Tr2. ..., consists of a base drive circuit 9 that drives the Tr6.

Figure 5(a) is a block diagram showing the U phase of the PWM inverter in Figure 4, where K^ is the gain of current amplifiers 3 and 4, Kn is the gain of the power amplifier, KN is the armature impedance, Kr represents current detection gain. Now, when the current command Ia is applied, a current In tb approximately equal to the current command ■σ flows, if the steady-state deviation is ignored.

By the way, depending on the accumulation time and turn-off time of the power transistors Tr+ to Trr, the power transistor Trl
- Upper and lower arms of Tr etc. (transistor Tr+ in Fig. 4)
and Tr2. Tr3 and ↑r4. Trs and Tr et al.) may be short-circuited. To prevent this arm short circuit, an on-delay circuit is generally provided in the base drive circuit 9 to delay the rise time of the drive signals of the transistors Tr+ to Trb by a certain amount.

However, the effect of this on-delay creates a dead zone. That is, a dead zone as shown in FIG. 5(b) occurs in the characteristics of the power amplifier represented by Kn in the block diagram of FIG. 5(a), and equivalently the gain Kn of the power amplifier becomes low. Zero-cross distortion as shown in FIG. 5(C) occurs, causing torque ripple and response delay, and hindering highly accurate motor control. Also, recently.

There is an increasing demand for reducing the current carrier ripple and noise by increasing the carrier frequency, and this is determined by the transistor used.Assuming the delay time is constant, as the carrier frequency increases, the above-mentioned current zero crossing Distortion and dead zones become larger, and torque ripple and response delays become more noticeable.

[Problem that the invention seeks to solve]

As a countermeasure for this, it is possible to compensate for the dead time by feeding back the inverter's output voltage and adding a voltage loop in addition to the current loop, or by adding a compensation amount to the current command assuming that the width of the current dead zone due to dead time is known in advance. By adding this, correction is made so that the current command does not fall into the dead zone. The former compensation method requires insulation of the feedback voltage in order to feed back the output voltage of the inverter, which has the disadvantage of complicating the circuit configuration. In addition, the latter method compensates by assuming that the width of the current dead zone due to dead time is known in advance, but in reality, the storage time of a transistor is determined by the width of the dead zone because the transistor junction temperature changes depending on the current amplification factor. It is necessary to consider that the width will change, and since the width of the dead zone changes when the carrier frequency changes, there are drawbacks such as the need to reset the correction amount each time.

In addition, in order to increase the gain of the current amplifier near zero current, the diode is non-conducting below the diode's on-voltage (approximately o, ev for silicon diodes), and when it is non-conducting, the feedback resistance of the operational amplifier is There is a method of inserting a diode in series with the feedback resistor of the current amplifier, taking advantage of the fact that the gain of the amplifier becomes higher as the resistance becomes equivalently higher, but with this method, the gain can be controlled when the diode is not conducting. This has the disadvantage that the stability of the current control system deteriorates.

An object of the present invention is to reduce the influence of the dead time of the on-delay circuit provided to prevent short-circuiting of the upper and lower arms of the power transistor, and to reduce the width of the current dead zone.
The purpose of the present invention is to provide a WM inverter.

[Means for Solving the Problems] The present invention provides a rise and fall of the drive signal for the power transistor in order to prevent short circuits between the upper and lower arms of the power transistor.
A triangular wave carrier signal for pulse width modulating the amplified current deviation between the current command and the feedback current in a PWM inverter having an on-delay circuit that delays the burnout time. The present invention is characterized in that it includes a triangular wave carrier signal generator that generates a low triangular wave carrier signal.

[Effect]

FIG. 3(a) shows the relationship between the triangular wave carrier signal of amplitude ec and the input voltage V+n (modulated voltage), and FIG. 3(b),
(c) shows inverter output 7hi pressure +Eo, -Eo.

Depending on the magnitude relationship between the triangular wave carrier signal and the input voltage V1m, the inverter generates an output voltage of 0Eo or -Eo at time 0 within one cycle T as shown in the figure.

Taking tI + t2 + t3, the upper arm of the transistor is on between t1 and t2, and L0-L1, t
2-t311tl, the lower arm of the transistor is on, as shown in FIGS. 3(b) and 3(c). Third
The shaded portions in FIGS. (b) and (c) indicate the time (dead time tj) in which none of the transistors in the upper and lower arms are turned on due to the on-delay of each transistor. As can be seen from Figures 3(b) and (C), the average output voltage of the inverter is not affected by dead time.
However, when the dead time relative to the carrier period T becomes a negative ratio (La/T), the proportion of transistors in the upper and lower arms that are turned off at the same time increases. In particular, in the region where the current command is small, the duty cycle approaches 50%, and if the on-delay is large, the pulse width modulation falls within the dead time L-, and around 50%, pulse width modulation is not possible and the current becomes insensitive. ;? occurs. On the other hand, if the carrier frequency is lowered.

Since the dead time is constant, its ratio to the carrier period T becomes small, and the dead zone of the 1rf flow is reduced.

What about lowering the carrier frequency? Since the lQ command is in a small region, noise does not increase due to a decrease in carrier frequency.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the PWM inverter of the present invention, and is a circuit diagram of a triangular wave carrier signal generator, and FIG. 2 is a waveform diagram of signals at each part thereof.

This triangular wave carrier signal generator consists of a comparator 21, an operational amplifier 22, and a resistor 2? , 28 and capacitor 23
A general triangular wave generation circuit composed of a window comparator composed of comparators 24 and 25,
An inverter 2B and an analog switch 23 (connected in parallel to a resistor 27) are added.

Therefore, when the current command 1a (voltage signal) enters the preset range -ΔV<Ia<+ΔV, the output of the window comparator becomes low level, and therefore the output of the inverter 26 becomes high level, and the analog switch 23
is turned on, both ends of the resistor 27 are shorted, and the operational amplifier 2
The period of the second output (carrier signal) becomes larger (the frequency becomes smaller). As a result, the ratio of the dead time to the carrier period becomes smaller, and the dead zone of the pulse-width-controlled current is reduced.

〔Effect of the invention〕

As explained above, the present invention reduces the effect of the dead time of the on-delay circuit by lowering the carrier frequency in a region where the current command is small, thereby reducing the current dead zone and improving the current responsiveness. It has the effect of being

[Brief explanation of drawings]

Figure 1 shows an example of a PWM inverter for an unfired IJ.
A circuit diagram of a triangular wave carrier signal generator. Figure 2 is a waveform diagram of each part of Figure 1. Figures 3 (a), (b), and (C) are the relationship between the carrier signal and input voltage Win and the waveform of the output voltage. Figure 4 is a diagram showing the configuration of a conventional PWM inverter.
5(a), 5(b), and 5(c) are a block diagram of the U phase of FIG. 4, a diagram showing the characteristics of the power amplifier, and a diagram showing the zero-cross distortion of the current, respectively. 21, 24, 25... comparator, 22...
Operational amplifier, 23... Analog switch, 26...
・Inverter, 2? , 2B...resistance, 29...
・Capacitor. Patent Applicant ('(Koshikikai t 1; Yasukawa, TI, Machine Works Agent: Wakabayashi Wakabayashi). IJ ″7/&-9 Figure 1

Claims (1)

[Claims] In a PWM inverter having an on-delay circuit that delays the rise time of a drive signal of a power transistor in order to prevent a short circuit between the upper and lower arms of the power transistor, the current deviation between the current command and the feedback current is amplified. A triangular wave carrier signal for pulse width modulating the
A PWM inverter comprising a triangular wave carrier signal generator that generates a triangular wave carrier signal having a lower frequency in a region where the current command is small than in other regions.