JPH10234187A - Pwm control apparatus for three-level inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a PWM control apparatus by which an output voltage can be controlled continuously, so as to be faithful to an instantaneous voltage command when a dipolar modulation and a partial dipolar modulation are used as the PWM control of a three-level inverter. SOLUTION: A bias-adjusting means is installed, in such a way that it is provided with a means by which fundamental modulated waves are divided into a positive instantaneous voltage command abp, used to generate positive output voltage pulses and into a negative instantaneous voltage command abn, used to generate negative output voltage pulses on the basis of a set bias amount and that the bias amount is adjusted in a period, in which the absolute value of either the positive instantaneous output voltage command or the negative instantaneous voltage command becomes a prescribed value or lower, i.e., a modulated-wave detector 24 which detects the absolute value is installed. Modulation-percentage, corresponding data 25 which is used to create a minimum on-pulse width decided by the characteristic to a switching element, is installed. A gain regulator 27 which finds a compensation gain according to the difference between the absolute value, and the modulation-percentage corresponding data is installed. A judging device 29 which judges modulation percentage used to create the minimum ON-pulse width is installed. Thereby, a bias compensation amount is computed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM control device for a three-level inverter for converting DC to AC, and more particularly to PWM control for continuously controlling an AC voltage.

[0002]

2. Description of the Related Art A three-level inverter divides a DC power supply voltage (an overhead line voltage) into two DC voltages by a capacitor connected in series, and outputs a positive (high potential), zero (intermediate potential) and negative (low potential). Three voltage levels are generated, and the three levels of voltages are selectively derived to an inverter output terminal by on / off operation of the main circuit switching element to control the output voltage. As a PWM control method of the output voltage of the three-level inverter, see, for example,
No. 6160, dipolar modulation (representing the output voltage by alternately outputting pulses via a zero voltage within a half cycle of the output voltage to express the output voltage), and unipolar modulation (single polarity during a half cycle of the output voltage). Are output, the output voltage is expressed by outputting a pulse, and partial dipolar modulation (a mode in which the dipolar modulation and the unipolar modulation are alternately mixed in the same cycle) is known. This PWM
In the control, as shown in FIG. 4, the bias B corresponding to the shift amount of the two modulated waves shifted positively and negatively is continuously varied according to the modulation rate A as shown in FIG. And the continuous transition of unipolar modulation is realized through partial dipolar modulation. FIG. 3 shows an example of the waveform of the modulated wave and the output voltage in the dipolar modulation region. In this PWM control, the positive / negative bias modulation waves abp and abn (FIG. 3) in which the basic modulation wave a (FIG. 3A) proportional to the output voltage fundamental wave is divided into two, and the amplitude is で and the bias B is shifted positive and negative by the bias B. 3 (b)) with positive and negative output voltage pulses (FIG. 3)
(C)) is used for the instantaneous command (instantaneous output voltage command). Here, the range of ± ΔA (shaded portion) in FIG. 3B is a region where the output pulse is narrower than the minimum on-pulse width determined by the characteristics of the switching elements forming the main circuit (FIG. 3C). Even if such a pulse width setting command is issued, the pulse width is limited to the minimum on-pulse width in this region, and P
This constitutes a WM control device.

[0003]

For this reason, in the above-mentioned conventional PWM control, the voltage of the hatched portion in FIG. 3B cannot be controlled, and the voltage ((()) shown in FIG. A / 2) − (B−ΔA)), the output voltage decreases. Such a voltage drop occurs when shifting from dipolar modulation to partial dipolar modulation. In particular, the amount of voltage drop is maximized immediately before shifting from dipolar modulation to partial dipolar modulation (indicated by the symbol “〇” shown in FIG. 4). ). For example, a carrier frequency of 3 kHz, an output voltage of 30% by dipolar modulation (one pulse which becomes a square wave voltage output is output voltage 1
00%. ), This voltage drop amount is about 3% at the maximum. Such a voltage drop causes problems such as fluctuations in output current and torque.

An object of the present invention is to provide a three-level inverter PWM control device capable of continuously controlling an output voltage faithfully in response to an instantaneous voltage command when dipolar modulation and partial dipolar modulation are employed as PWM control. Is to do.

[0005]

The object of the present invention is to convert a DC voltage into an AC phase voltage having three potentials of a positive voltage pulse, a negative voltage pulse, and a zero voltage by PWM control and to lead the AC voltage to an AC terminal. In a PWM control device of a three-level inverter, the problem is solved by providing a means for adjusting the bias characteristics in a direction to increase the bias characteristic during a period in which the absolute value of one of the positive and negative instantaneous output voltage commands is equal to or less than a predetermined value. Here, the means for adjusting the bias characteristic in a direction to increase the bias characteristic is a period in which positive and negative voltage pulses are alternately output via zero voltage, and the PWM-controlled output pulse is limited to a minimum pulse width. In the region, a pulse smaller than the minimum pulse width is not generated. This makes it possible to continuously control the output voltage faithfully according to the instantaneous output voltage command.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows one embodiment of the present invention.
This is a PWM control device for the level inverter. In FIG. 1, G denotes a train line (an overhead line) which is a DC voltage source, 61, 62.
Is a capacitor (voltage dividing capacitor) divided from the voltage of the DC voltage source G to generate an intermediate voltage (neutral point voltage) corresponding to zero potential on the AC output side. Here, the voltage of the voltage dividing capacitor is assumed to be Ed / 2. Reference numerals 70 to 73 denote self-extinguishing switching elements provided with a rectifying element for reflux (in this example, IGBTs are used, but GTOs and transistors may be used). Reference numerals 74 and 75 derive neutral point voltages of capacitors. It is an auxiliary rectifying element, and a switching arm for one U phase is constituted by 7a. 7b and 7c constitute switching arms for the V phase and the W phase, respectively, similarly to the switching arm 7a. Reference numeral 8 denotes a load, which is a case of an induction motor. Switching arms 7a to 7c
Can operate independently for each phase, and generate three levels of output voltages by selective on / off control of switching elements. (Note that the details of the main circuit of the three-level inverter are disclosed in Japanese Patent Application Laid-Open Nos.
74088 and the like, and details of PWM control are described in JP-A-3-301512 and the like. )

Next, the PWM control unit will be described. In FIG. 1, a fundamental wave voltage command generator 1 inputs a frequency command Fi * of an inverter output voltage, and a SIN generator 11
, An output voltage effective value command E * and a DC voltage Ed are input, a fundamental wave amplitude command value A (modulation rate) A is output via the amplitude setting device 12, and a multiplier 13 is output via the multiplier 13. To obtain the instantaneous inverter output voltage command A · sin 求 め and output it to the amplitude command distributor 2. Amplitude command distributor 2
Calculates the inverter output voltage command A · sinΘ
The bias amount B set by the bias setting unit 21 in accordance with the fundamental wave amplitude command value A (modulation rate) is added or subtracted by the adder 22.
To generate a positive bias command abp and a negative bias command abn. The polarity discriminating distributor 3 converts the positive bias command abp and the negative bias command abn into the signal distributors 30, 31, 33, and 34 and the adders 32 and 35.
Positive and negative voltage commands for positive and negative pulses ap and an
Distribute to The pulse generator 4 receives the positive and negative voltage commands ap and an, generates PWM signals for the main circuit switching elements 70 and 73, inverts these signals, and outputs a one-phase P signal.
Generate WM signals S1 to S4. In response to these PWM signals, the gate logic unit 5 generates a PWM pulse train in which the minimum on / off time is secured and the non-wrap time for preventing element short-circuiting is managed, and the main circuit is controlled via a gate driver (not shown). Send a gate signal to the switching element.

In this embodiment, the positive bias command abp
A modulated wave detector 24 for detecting the absolute value of the negative bias command abn, modulation rate equivalent data △ A25 for creating the minimum on-pulse width, a subtractor 26, a gain adjuster 27 for obtaining a compensation gain △ B, a multiplier 28, And bias setting unit 21
A determination unit 29 for generating determination signals from A1 to A2 of the modulation rate A shown in FIG. 4 (A1 to A2 is “1” and others are “0”) is provided, and a positive bias command abp is provided. In the region where the magnitude of the negative bias command abn is equal to or less than the modulation rate for creating the minimum on-pulse width,
The operation for correcting the bias B is performed. That is, the positive side bias command abp and the negative side bias command abn are input to the modulation wave detector 24, where the absolute values of abp and abn are detected, and the modulation rate equivalent data { The difference ２６a from A25 is obtained by the subtractor 26, and the required compensation gain △ B corresponding to the difference △ a is obtained from the gain adjuster 27. On the other hand, the determination signal from the bias setting unit 21 from the A1 of the modulation factor A shown in FIG. 4 to A2 made by determination unit 29, a multiplier 28 △ B and multiplier to bias amount B output △ B ₁₀ obtained Is added to. Therefore, the bias characteristic after the correction is determined by the output of the multiplier 28 △ B ₁₀
Are added to obtain a bias characteristic as shown in FIG. As a result, the positive / negative bias command operates so as not to enter the voltage region ± ΔA of the hatched portion in FIG. As a result, in the present embodiment, it is possible to secure a predetermined output pulse wider than the minimum on-pulse width determined by the characteristics of the switching element. Therefore, it is possible to continuously control the output voltage faithfully in response to the instantaneous voltage command. The error between the command and the actual voltage is reduced.

FIG. 5 shows another embodiment of the present invention. This embodiment is different from the embodiment of FIG.
91 is provided to easily perform voltage correction without detecting the positive bias command abp and the negative bias command abn. Other configurations are the same as those of the embodiment of FIG. The bias corrector 291 calculates the modulation factor A shown in FIG.
Determined by calculating the correction amount △ B ₂₀ from 1 to A2. FIG.
In the bias setting unit 21, the modulation factor A shown in FIG.
A1 and A2 can be known, so that the correction amount △ B from A1 to A2 calculated by the bias corrector 291 can be obtained.
₂₀ is added to the bias amount B. Thereby, the same effect as that of FIG. 1 can be obtained.

Although the embodiment of the present invention has been described with reference to an induction motor as an example, the same applies to other AC motors. Although the embodiments of the inverters are described here, the output terminals of these inverters can be connected to an AC power supply via a reactance element to operate as a self-excited converter that converts AC to DC (regeneration operation). It is. In this case, the same effect as that of the inverter can be expected. Naturally, if a microprocessor or the like is used, a part or all of the pulse generating means can be programmed and realized as software.

[0011]

As described above, according to the present invention,
In a period in which positive and negative voltage pulses are alternately output via the zero voltage, and in a region where the PWM-controlled output pulse is limited to a minimum pulse width determined by the characteristics of the switching element, a pulse having a width equal to or less than the minimum pulse width is output. Since the bias characteristic is adjusted so as not to generate the output voltage, it is possible to control the output voltage faithfully according to the instantaneous output voltage command, and it is possible to realize continuous control of the output voltage.

[Brief description of the drawings]

FIG. 1 shows a PWM control apparatus for a three-level inverter according to an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of bias correction in FIG. 1;

FIG. 3 is a diagram illustrating voltage correction.

FIG. 4 is a diagram illustrating an output voltage of a three-level inverter.

FIG. 5 is a configuration diagram showing another embodiment of the present invention.

[Explanation of symbols]

1. Basic wave voltage command generator, 2. Amplitude command distributor, 3.
Polarity discriminating distributor, 4 pulse generator, 5 gate logic unit, G DC voltage source, 7a, 7b, 7c switching arm, 8 induction motor, 21 bias setting unit, 24
... Modulated wave detector, 27 ... Gain adjuster, 29 ... Determiner,
291, a bias corrector, 30, 31, 33, 34 ... a signal distributor, 61, 62 ... a voltage dividing capacitor, 70 to 73 ...
Switching element, 74, 75 ... auxiliary rectifying element

Claims (4)

[Claims] 1. A PWM control apparatus for a three-level inverter that converts a DC voltage into an AC phase voltage having three potentials of a positive voltage pulse, a negative voltage pulse, and zero voltage by PWM control and leads the AC voltage to an AC terminal. Having a means for dividing into a positive instantaneous voltage command for generating a positive output voltage pulse and a negative instantaneous voltage command for generating a negative output voltage pulse by a bias amount that sets the basic modulation wave, A PWM control device for a three-level inverter, comprising: a bias adjusting means for adjusting the bias amount during a period in which the absolute value of one of the positive and negative instantaneous output voltage commands is equal to or less than a predetermined value. 2. A method according to claim 1, wherein said bias adjusting means has a minimum on-pulse width determined by characteristics of a modulation wave detector for detecting an absolute value of one of positive and negative instantaneous output voltage commands and a switching element forming an inverter. The modulation rate equivalent data to create, the gain adjuster to determine the compensation gain according to the difference between the absolute value and the modulation rate equivalent data, and a determiner to determine the modulation rate to create the minimum on-pulse width, A PWM control device for a three-level inverter, which calculates a bias compensation amount. 3. A PWM control apparatus for a three-level inverter which converts a DC voltage into an AC phase voltage having three potentials of a positive voltage pulse, a negative voltage pulse and zero voltage by PWM control and leads the AC voltage to an AC terminal. Having a means for dividing into a positive instantaneous voltage command for generating a positive output voltage pulse and a negative instantaneous voltage command for generating a negative output voltage pulse by a bias amount that sets the basic modulation wave, A bias correction means for adjusting the bias amount for a predetermined period is provided.
WM control device. 4. A method according to claim 3, wherein said bias correction means calculates a bias correction amount in a modulation rate period for generating a minimum on-pulse width determined by characteristics of a switching element forming an inverter.
PWM controller for level inverter.