JP3197594B2 - Switching method of current source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching method for a current source inverter.

[0002]

2. Description of the Related Art There are two types of inverter circuit systems, a voltage type and a current type. The current type has the advantage that protection is easier and high reliability can be obtained as compared with the voltage type, while the commercial type as a power supply At present, voltage-type inverters are the mainstream because the converter is a voltage source, and the converter that creates the current source also needs to perform control. Also, CVC
In order to make the output voltage and current close to a sine wave in the F inverter, PWM control is performed, and furthermore, the carrier frequency is increased. FIG. 3 shows a 5-pulse mode output current and a voltage waveform of a current type PWM inverter described in “Semiconductor Power Conversion Circuit” PZ152 (edited by the Institute of Electrical Engineers of Japan, published by Ohmsha, 1987). The pulse width α1 shown in FIG.
The content of the low-order harmonics of the output current and voltage changes depending on α2, and specific low-order harmonics can be eliminated by appropriately determining α1 and α2.

[0003]

In the above-mentioned example, even if the number of pulses is increased to 9 pulses, the 19th, 23rd, and 25th harmonics will not
When the VVVF inverter is applied to a motor drive, torque ripple occurs. When applied to a CVCF inverter, the voltage distortion rate is large and cannot be put to practical use. The output voltage is controlled by changing the DC current. This DC current control is usually performed by a thyristor converter, and the thyristor converter has poor response, so that it is difficult for the inverter to respond at high speed. Further, the pulse pattern is usually written in the ROM, and there is a problem that the control circuit becomes complicated such as requiring a CPU. On the other hand, it is conceivable to increase the number of pulses to reduce the harmonic components. However, since the PWM control is not performed during the 60-degree period, the harmonic components cannot be eliminated in principle, and the memory capacity of the ROM for storing the pulse pattern is also reduced. There is a problem that increases.

[0004]

A control method of a current source inverter according to the present invention controls an instantaneous value of a control amount so that an error between the control amount and a command value falls within a predetermined allowable value. For this purpose, the allowable value of the error is set by the hysteresis value of the hysteresis comparator, and the switching pattern is changed so that the error decreases at the moment when the error reaches the allowable value and the output of the hysteresis comparator changes. At this time, in determining which switching pattern is selected, two hysteresis comparators having different hysteresis values for each phase are used to determine the magnitude of the error between the three phases. Output voltage control is performed by using a reflux mode in which the upper and lower arms are short-circuited, and the converter is controlled so that the DC current is substantially constant.

[0005]

According to the control method of the present invention, since the control amount always follows the command value within the allowable value, if the command value is a sine wave, a good sine wave output containing almost no low-order harmonics can be obtained. can get. The pulse width of the inverter output current is
The hysteresis comparator has the same output state duration, and the commutation time is when the output of the hysteresis comparator changes.Therefore, there is no need for a ROM or the like that stores the pulse pattern, and it is easily controlled by the hysteresis comparator and the logic circuit. A circuit can be configured.

[0006]

FIG. 1 shows an embodiment in which the present invention is applied to a CVCF inverter. Converter 2 and reactor 3
This makes the power from the commercial power supply 1 a constant current, and each phase has two switching devices UP for an upper arm and a lower arm.
, UN, VP, VN and WP, WN, the three-phase full-bridge inverter having six switching devices 4 requires a sine-wave output voltage. Control. The difference between the capacitor voltage detected by the voltage detector for each phase and the voltage command from the command voltage generator 10 is obtained by the subtractor 9, and the hysteresis comparators 8a and 8b
To enter. The hysteresis comparator 8a has a hysteresis value ± Hw, and the hysteresis comparator 8b has a hysteresis value ± Hn (Hw>Hn> 0), and outputs Cwj, Cnj (j = u, v, j) of each hysteresis comparator.
w) becomes "H" when the error exceeds + Hw, + Hn, and becomes "L" when the error exceeds -Hw, -Hn. The switching pattern determining circuit 7 determines a switching pattern according to Table 2 according to the outputs of the six hysteresis comparators.

FIG. 2 shows a U-phase voltage command Vu ^* and an output voltage V
7 shows a relationship between an error from u (hysteresis comparator input) and a hysteresis comparator output. (a) is a hysteresis comparator input, (b) is the output of the hysteresis comparator 8b, (c) is the output of the hysteresis comparator 8a, and as can be seen from (a), the voltage error is within the hysteresis value ± Hw. By appropriately setting the hysteresis value, a good sine wave output voltage with less harmonic components can be obtained. The switch drive circuit 6 generates a switch drive signal for realizing the switching pattern selected by the switching pattern determination circuit 7. When the present invention is applied to a VVVF inverter, the voltage detector may be replaced with a current detector and the voltage command may be replaced with a current command in FIG.

[0008]

As described above, according to the control method of the present invention, it is possible to obtain an accurate output waveform with a simple control configuration. Further, since the output control is performed by the inverter, a high-speed response is possible without using the converter in the PWM control, and the output is not affected even if there is a slight pulsating current in the DC current.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main circuit diagram and a control configuration when the present invention is applied to a CVCF inverter.

FIG. 2 is a diagram illustrating a relationship between a voltage error and an output of a hysteresis comparator for a U phase.

FIG. 3 is a diagram illustrating the operation of a conventional five-pulse inverter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Converter 3 Reactor 4 Switching device 5 Filter capacitor 6 Switch drive circuit 7 Switching pattern decision circuit 8a, 8b Hysteresis comparator 9 Subtractor 10 Command voltage generator

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideo Sekimoto 4-6-32 Higashikashigaya, Ebina-shi, Kanagawa Toyo Electric Manufacturing Co., Ltd. Sagami Factory (56) References JP-A-63-95856 (JP, A) ( 58) Surveyed field (Int.Cl. ⁷ , DB name) H02M 7/48

Claims (1)

(57) [Claims] 1. A three-phase full-bridge inverter comprising a current source and six switching devices, a filter capacitor for smoothing an output voltage, and three detections for detecting control amounts of U, V, and W phases. , Three subtractors for calculating an error between a command value generated by a command generator and a control amount detected by the detection value for each phase, and a hysteresis using the error signal of each phase as an input Values ± Hw, ± Hn (Hw
>Hn> 0), and outputs Cwj and Cnj of the hysteresis comparator.
(J = u, v, w) is set to "H" when the input exceeds Hw, Hn for all phases, and to "L" when the input exceeds ─Hw, ─Hn. The output of the hysteresis comparator In a current source inverter including a switching pattern determining circuit for determining a switching pattern of an inverter switch according to a state and a switch driving circuit for driving a switching device on / off, nine types of switching for driving six switching devices on / off Let Pk = {Su, Sv, Sw} (where k = 1-9) where Sj (j = u, v, w) is 10 when the upper arm switch is on and the lower arm switch is When OFF, the upper arm switch is OFF, and when the lower arm switch is ON, the upper and lower arms are ON when 11, and when 00, both upper and lower arms are OFF. Te, when the Sj corresponding to the Pk was Table 1, Table 1] As shown in Table 2, the switching pattern deciding circuit changes according to the output state of the hysteresis comparator. A switching method for a current source inverter, characterized by determining a switching pattern.