JPS6231375A - Pwm inverter - Google Patents

Abstract

PURPOSE:To alleviate a waveform distortion by reducing a slope near zero of a triangular carrier signal to reduce the width of a current insensitive band due to an ON delay. CONSTITUTION:A triangular carrier signal generator of PWM inverter has a triangular signal generator 20 having a comparator 21, an operational ampli fier 22, a capacitor 27, and resistors 31-34, and outputs a triangular carrier signal Vout. An inverting comparator 25, an analog switch 26, a window compa rator having comparators 23, 24, and a resistor 37 are added to the generator 20. Thus, when the signal Vout fall within a range of -DELTAV<Vout<DELTAV, the switch 26 is turned ON to connect the resistor 37 in parallel with the resistor 32 to reduce the slope of the signal Vout. As a result, the gain of the power amplifier of this range is increased to reduce the width of a current insensitive band due to an ON delay.

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 four power transistors in the case of direct current control, and becomes a drive signal for six power transistors in the case of alternating current control.

FIG. 5 is a configuration diagram of a conventional example of an AC current controlled PWM inverter, and this conventional example has six power transistors Tr.
t, Tr2. Tr3. Trm, Trs.

Tr&, diode DI, 02.03.04. I
IS, 06, an inverter power circuit 1 that drives the motor 2, a current amplifier 3 that amplifies the deviation between the current command ■σ and the current detection signal (feedback current) Inrb, and a current amplifier 3 that amplifies the deviation between the current command ■σ and the current detection signal (feedback current) Inrb; feedback current)
■A current amplifier 4 that amplifies the deviation of the current amplifier 3.4, a current calculation circuit 5 that generates a current 1w' from the outputs In' and It' of the current amplifier 3.4, and a triangular wave carrier signal generator! 0 and
The outputs In' and Ima0゜1 of the current calculation circuit 5, respectively.
Comparator 6.7 that compares the voltage of w0 with the carrier signal
．． 8 and the output of the comparator 6.7.8, the power transistors Tr+, Trz,..., Tra
It consists of a base drive circuit 9 that drives the.

Figure 6(a) is a block diagram showing the U phase of the PWM inverter in Figure 5, where K^ is the gain of current amplifiers 3 and 4, Kn is the gain of the power amplifier, Ks is the armature impedance, K! represents the current detection gain. Now, when the current command ■σ is applied, if the steady-state deviation amount is ignored, the current IIIf- is almost equal to the current command In.
flows.

By the way, depending on the accumulation time and turn-off time of the power transistor Tr+-Tr6, the power transistor Tr+-
The upper and lower arms of Tri (transistor Trs in Figure 5)
and Trz, ↑ "3 and Tra, Trs and Tra)" may be short-circuited. To prevent this arm short-circuit, generally the base drive circuit 9 is configured to delay the rise time of the drive signals of transistors Tr1 to Tr6 by a certain amount. An on-delay circuit is provided.

However, the effect of this on-delay creates a dead zone. That is, a dead zone as shown in FIG. 6(b) occurs in the characteristics of the power amplifier represented by Kn in the block diagram of FIG. 6(a), and the gain Kn of the power amplifier becomes equivalently lower. Zero-cross distortion as shown in FIG. 6(C) occurs, causing torque ripple and response delay, and hindering highly accurate motor control. In addition, recently there has been a growing demand for higher carrier frequencies to reduce current carrier ripple and noise, and as this is determined by the transistor used, if the on-delay time is constant, as the carrier frequency increases, The current zero-cross distortion and dead zone become larger, and torque ripple and response delay 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 has the disadvantage that the feedback voltage needs to be insulated to feed back the output voltage of the inverter, making the circuit configuration complicated. 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.1. Furthermore, since the width of the dead zone changes when the carrier frequency changes, there is a drawback that the correction amount must be reset each time.

In addition, in order to increase the gain of the current amplifier near zero current, the diode is non-conducting below the on-voltage of the diode (approximately O, SV for silicon diodes), and when this non-conducting state, the feedback resistance of the operational amplifier is equivalent to There is a method of inserting a diode in series with the feedback resistor of the current amplifier to take advantage of the fact that the current resistance becomes high and the gain of the amplifier becomes high. However, with this method, it is not possible to control the gain 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 problems]

In order to prevent a short circuit between the upper and lower arms of the power transistor, the present invention uses a PWM inverter that includes a power transistor and an on-delay circuit that delays the rise time of the evening drive signal to prevent the amplified current deviation between the current command and the feedback current. The present invention is characterized by comprising a triangular wave carrier signal generator that generates a nonlinear triangular wave carrier signal for pulse width modulation, the slope of which is smaller near zero than in other parts.

[Effect]

Figure 3 (a) shows the relationship between the triangular wave carrier signal of vibration [eC and the input wood pressure Van (modulated voltage)], and Figure 3 (b) shows the waveform of the pulse width modulated inverter output voltage. . In FIG. 3(a), the magnitude relationship between the triangular wave carrier signal and the input voltage vIt+ is compared, and the triangular wave carrier signal is +Eo in the smaller region and -Eo in the larger region.
An output voltage of Eo is generated and the average output voltage within this carrier period is controlled.

The relationship between the input voltage VIt+ and the inverter output average voltage Eat pulse width modulated by the carrier signal will be explained with reference to FIG.

As shown, at time 1o, 1. ．． 12, the slope of the carrier signal is between time 10.11 and time 1.12. , 12 are different, but they are symmetrical with respect to time t1, and when considering the average output voltage Eoma, instead of considering the period of JIT of the carrier signal, it is sufficient to consider the period of T/2. Therefore, , time 10.1. The relationship between the input voltage V1m and the average output voltage Eoma between the two is determined. If the power supply voltage of the inverter is 2Eo, when the upper arm transistor is turned on, a voltage +Eo is output, and when the lower arm transistor is turned on, a voltage -Eo is output.

With time t0 as the origin, the carrier signal at time 1 (10≦and≦1+) is expressed by the following formula%Formula %(1) Since v=V+n at time t, from equation (1), e
e VI++ = et ec −-・
-φ (2) From formula (2), formula % formula % (4) As can be seen from formula [4], the average output voltage Eo is the amplitude ec of the carrier signal and the input voltage vI! It is proportional to the ratio of I. Therefore, the 61st iii! The gain Ka of the power amplifier in (a) is 5° (5) ec.

It can be seen that in order to increase the gain KB of this power amplifier, the amplitude ec of the carrier signal should be made small.

FIG. 4(a) shows an example of a waveform of a carrier signal in which the slope near zero is changed in order to increase the gain Ka of the power amplifier in a region where the input voltage V1m is low. In this example, the input voltage vII+ is -VTL≦vItI≦Vto
In the range, the amplitude of the carrier signal is set to 115, and (
From equation 5), the power amplifier gain of 8 is about 5 times that of the conventional one. FIG. 4(b) shows the characteristics of the average output voltage Eat with respect to the input voltage Vifi when this carrier signal is used. Therefore, 'tfli, the gain near command zero can be increased five times, and the influence of the dead zone can be reduced to 1.
15, and since the flowing current is fully commanded in the '\L flow direction, the zero cross distortion is also reduced.

〔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 each part thereof.

This triangular wave carrier signal generation circuit consists of a comparator 21
and operational amplifier 22, capacitor 27, and resistors 31 to 34 (
Operational amplifier 22. The capacitor 27 and the resistor 32 constitute an integrator), and the triangular wave carrier signal Voot
The output signal VCOMP of the comparator 21 is inverted to a general triangular wave signal generation circuit 20 that outputs
The output of the comparator 25 and the comparator 25 and the resistor 37
and a comparator 23 that outputs a control signal VIIIND that turns on the analog switch 2B only when the triangular wave carrier signal Voot enters the region of 1 ΔV < Voot > ΔV.
, 24 and a resistor 36 are added.

Therefore, the carrier signal VOOT is -Δv Vout
When entering the region <ΔV, the analog switch 26 is turned on, the resistor 37 is connected in parallel to the resistor 32, and the slope of the triangular wave carrier signal VoσT becomes small.

As a result, the gain of the power amplifier in this region increases, and the width of the current dead zone due to the on-delay decreases.

Note that the value of the capacitor of the integrating circuit may be changed instead of the resistor.

〔Effect of the invention〕

As explained above, the present invention reduces the slope of the triangular wave carrier signal near zero, thereby increasing the current loop gain near zero current, reducing the width of the current dead zone due to on-delay, and reducing waveform distortion. As a result, torque ripple and response delay are eliminated, highly accurate motor control becomes removable, and even if the carrier frequency is changed, there is no need to worry about having to reset the correction amount.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the PWM inverter of the present invention, and shows a circuit diagram of a triangular wave carrier signal generator, Fig. 2 is a waveform diagram of each part of Fig. 1, and Fig. 3 (a) and (b) show a triangular wave carrier signal generator. Figures 4(a) and 4(b) are diagrams showing the relationship between signals and input voltages and the waveform of the inverter output voltage. Figures 4(a) and 4(b) show an example of the waveform of a carrier signal with a slope near zero, and the average value for the input voltage Vla using this carrier signal. Figure 5 shows the configuration of a conventional PWM inverter; Figures 6 (a), (b), and (c) are block diagrams of the U phase in Figure 5, respectively. , a diagram showing characteristics of a power amplifier, and a diagram showing zero-cross distortion of current. 21.23, 24.25... Comparator, 22...
- Operational amplifier, 26...analog switch. 27... Capacitor, 31.32, 33, 34.38.37... Resistor, Vo
σDing: Carrier signal, -ΔV, +ΔV: Voltage value that determines the nonlinear range. Figure 1 Figure 2 Figure 3 (a) (b) Figure 4

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 nonlinear triangular wave carrier signal with a slope near zero that is smaller than other parts.