JPH02101968A - Voltage type multiple inverter - Google Patents

Abstract

PURPOSE:To reduce the number of controller and to enable usage of a standard output transformer by providing an inverter with a controller for performing pulse width modulation common to all inverters, a time difference generating means and another transformers on the AC side then connecting the secondaries of transformers in series. CONSTITUTION:A controller 13 for performing pulse width modulation common to the inverters 3, 4 and a time difference generating means 14 for providing firing signals to the inverters 3, 4 with the same time difference are provided. Transformers 11, 12 are arranged independently on the AC side, with the secondary sides thereof connected in series. By such an arrangement, the number of controllers can be reduced and a standard output transformer can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage source multiplex inverter that uses a plurality of voltage source inverters in a multiplex manner.

[Conventional technology]

FIG. 4 is a main circuit connection diagram showing a conventional example of multiplexing voltage source inverters, and shows a case where two inverters are multiplexed and used.

In a voltage source inverter, the output AC voltage waveform is a square wave, so by combining multiple square waves through multiplexing, harmonics are reduced and step changes in voltage are reduced, creating a waveform that is more similar to a sine wave. It is something to do.

In the conventional circuit shown in FIG. 4, there are a first inverter 3 and a second inverter 4 that receive DC power from a DC power source 2, and these inverters 3 and 4 are controlled by their respective attached controllers. By the action of devices 5 and 6, input DC power is separately converted into AC power. At this time, the second inverter 4 is π
It operates with a phase delay of /6 (ie, 30 degrees).

The AC output of the first inverter 3 is output via the first transformer 7, which has a star-shaped connection on the secondary side, and the AC output of the second inverter 4 has a star-shaped connection on the secondary side. This second transformer 8 has a winding configuration that can cancel the phase delay of π/6 of the AC power output from the second inverter 4. There is.

Therefore, the secondary side of the first transformer 7 and the secondary side of the second transformer 8
The next side is connected in series to supply AC power to the load 9.

In other words, is it not accompanied by a phase shift in the output AC voltage? With respect to the A1 inverter 3, the fundamental wave component of the output voltage of the second inverter 4 has a phase delayed by π/6 with respect to the fundamental wave component output from the first inverter 3. 8 causes the phase to advance by π/6, resulting in the same phase on the load side, but in this way the two inverters 3
12 by multiplexing and operating 4 and 4 out of phase.
It becomes a pulse inverter.

The conventional example circuit shown in Fig. 4 is a case where two three-phase inverters are multiplexed, so it is operated with a phase difference of π/6, but it is possible to multiplex N three-phase inverters. in case of,
If each is operated with a phase difference of π/(3・N) and the output transformer cancels this phase difference, the inverter will have a pulse count of 6N, reducing harmonics and increasing the voltage. The step change can be significantly reduced to a more sinusoidal waveform.

[Problem to be solved by the invention]

As mentioned above, when multiplexing and operating multiple voltage source inverters, it is necessary to maintain a predetermined phase difference between them. requires separate control equipment. Furthermore, in order to cancel the phase difference set during inverter operation with a transformer provided on the output side of the inverter, a transformer having a structure that advances the phase is required.

Therefore, in order to multiplex and operate a plurality of voltage source inverters, each inverter must be provided with a control device and a non-standard transformer must be prepared.

Therefore, the purpose of this invention is to reduce the number of control devices for these voltage source inverters and to enable the use of standard output transformers when multiple voltage source inverters are operated in a multiplex manner. be.

[Means to solve the problem]

In order to achieve the above object, the voltage source multiplex inverter of the present invention generates a common pulse width modulation signal for each inverter in order to perform pulse width modulation control of a plurality of voltage source inverters that convert direct current to alternating current. A control device, a time difference generating means for applying an ignition signal based on the pulse width modulation signal to each inverter with the same time difference, and a transformer separately connected to the AC output side of each of the inverters. , the secondary sides of this transformer are connected in series.

[Function] This invention suppresses low-order harmonics and suppresses step changes in voltage, which are the objectives of multiplexing voltage source inverters, and the former is achieved by pulse width modulation (hereinafter referred to as PW), which is a conventional technology.
(abbreviated as M) control, the latter, that is, the step change in voltage, is suppressed by giving the ignition signal to each inverter with the same time difference, but the point of giving it to each inverter is Since the arc signal is a time difference rather than a phase difference, the inverter control device can be shared and a standard type transformer can be used.

〔Example〕

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention, and shows a case where two inverters are multiplexed and operated.

In this FIG. 1, the first inverter 3 is connected to the DC power supply 2.
DC power is converted into AC power by PWM control, and this AC power is outputted via the first transformer 11 whose secondary side is star-connected, and the second inverter 4 similarly. After converting DC to AC using PWM control, the first
AC power is output through a second transformer 12 having the same structure as the transformer 11 . Therefore, the secondary side of the first transformer 11 and the secondary side of the second transformer 12 are connected in series, and this AC power is supplied to a load 9 common to both.

On the other hand, the first inverter 3 and the second inverter 4 are turned on and off by a pulse width modulated firing signal from a common control device 13, and the first inverter 3 is controlled by this control. The second inverter 4 is operated by directly inputting the output signal of the device 13, while the second inverter 4 is operated by the time difference generator 1.
The output signal of the control device 13 is inputted via 4.

That is, the second inverter 4 operates with a fixed time delay with respect to the first inverter 3.

FIG. 2 is a waveform diagram showing the inverter output voltage waveform in the embodiment circuit shown in FIG. 2. The output voltage waveforms of the inverter 4 and FIG. 2(c) show the voltage waveforms of the load 9, respectively.

As shown in FIG. 2, by applying a base signal having a constant time difference to the first inverter 3 and the second inverter 4, the load 9 connected by the transformers 11 and 12 is
It can be seen that the amount of step change in voltage is reduced by half compared to the case without time difference (see FIG. 2 (c)).

FIG. 3 is a waveform diagram showing the inverter input signal waveform in the embodiment circuit shown in FIG.
, respectively, generate a PWM signal input to the second inverter 4.

As shown in FIG. 3, by the action of the time difference generator 14, the inverters can be operated with a constant time difference by simply installing one control device common to each inverter, and as a result, the voltage step The amount of change is significantly suppressed.

〔Effect of the invention〕

According to this invention, when multiplexing and operating a plurality of voltage source inverters, only one control device that performs PWM control is installed in common for each inverter, and the signals from this control device are By distributing the voltage to each inverter at a predetermined time difference through a means, it is possible to suppress voltage step changes, which is one of the purposes of multiplexing inverters, with a simpler configuration than in the past (i.e., one control device for multiple inverters). Since this can be achieved with only one unit), the entire device can be made smaller and lower in price. Furthermore, there is no need for the output transformer to have a phase advancing structure, and standard transformers having the same structure can all be used.

[Brief explanation of the drawing]

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the inverter output voltage waveform in the embodiment circuit shown in FIG. 1, and FIG. FIG. 4 is a waveform diagram showing an inverter input signal waveform in an example circuit, and FIG. 4 is a main circuit connection diagram showing a conventional example of multiplexing voltage source inverters. 2... DC power supply, 3... First inverter, 4...
Second inverter, 5, 6.13...control device, 7.1
1... 1st transformer, 8, 12... 2nd transformer, 9 river load, 14... time difference generator. 31 Figure 3

Claims (1)

[Claims] 1) In order to perform pulse width modulation control of multiple voltage source inverters that convert DC to AC, a control device that generates a common pulse width modulation signal for each inverter, and an ignition signal based on this pulse width modulation signal. , a time difference generation means for giving the same time difference between each inverter, and a transformer separately connected to the AC output side of each inverter, and the secondary sides of the transformers are connected in series. Features: Voltage source multiplex inverter.