JPH04200203A - Control method for voltage type vvvf inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling a voltage type VVVF (Variable Voltage Variable Frequency) inverter suitable for use, for example, in driving a DC electric vehicle.

[Conventional technology]

The applicant has previously proposed voltage source inverters connected in series on the DC input side. FIG. 5 is a schematic diagram showing Kagaru's proposed method.

In the figure, 1 is an overhead contact line, 2 is a rail, and 3 is an input filter reactor. This input filter reactor 3
Normally, a switch or the like is connected to the power supply side of the switch, but it is not particularly relevant here, so its illustration is omitted. 41.42 is inverter unit inverter 411,421
and input capacitors 412, 422, etc., and a vehicle drive motor 51, 52 as a load is connected to the unit inverters 411, 421.

FIG. 6 is a time chart for explaining the operation of FIG. 5.

In the same figure, S is Uni7) Inverter 411°421
The frequency of the control signal is f□, and here it is assumed that both inverters are controlled by the same control signal.

1411+i4□ is the input current waveform of the unit inverter. v412+v4□2 are voltage waveforms of the input capacitor, each including a frequency ripple of 6f. The input voltage waveform of the inverters connected in series is expressed as a combination of V412 and v4□2, and has a waveform as shown by e.

Since both inverters are controlled by the same phase control signal,
The input terminal ripple is also in the same phase and is twice that of the inverter unit.

By the way, when driving a DC electric car with such an inverter, an alternating current due to voltage ripple on the inverter input side flows through the overhead contact line and track circuit, but this alternating current has different frequencies at each frequency due to its influence on the track circuit signal. There is a limit value corresponding to this, and this is limited by the input filter reactor.

Also, the frequency of the track circuit signal is f, 1/2fs
(f is the commercial power frequency of 50Hz or 60Hz)
Therefore, when f, , = 50Hz, the pull frequency is 2 when the inverter frequency is 4.17Hz.
When it is 5Hz and 8.33Hz, it becomes 50Hz. Therefore, the reactor value is 4.17, 8.33H
The value is selected so that it does not affect the track circuit etc. when z. In other words, in the case of an inverter electric train, the pull frequency changes, so the inductance of the reactor is about twice that of a chopper electric train, and the weight is also larger.

[Problem to be solved by the invention]

As described above, in conventional inverter electric trains, the weight of this input filter reactor occupies a large proportion of the entire inverter system, and therefore it is desired to reduce its weight.

Therefore, an object of the present invention is to reduce the ripple voltage of the input capacitor and to reduce the capacitance and size of the input filter reactor.

[Means for Solving the Problem] The above-mentioned method is applied to a voltage-type VVVF inverter formed by connecting two or more sets of voltage-type unit inverters that are individually controlled to drive a load in series on their DC input sides. Control signals for controlling each unit inverter constituting the group are controlled by giving a phase difference to each other.

[Function] Focusing on the fact that the PWM/control of each inverter connected in series can be performed completely independently, by creating a phase difference between the control signals of PWM control between each inverter, the ripple pull of each input capacitor is reduced. A phase difference is also created in the voltage, so that the ripple voltages cancel each other out.

This significantly reduces the combined ripple voltage of the series-connected inverters.

Example C) FIG. 1 is an explanatory diagram for explaining the present invention in detail.

Note that the inverter system used here is the same as that shown in FIG.

In FIG. 1, Sl is a control signal for the unit inverter 411, and S2 is a control signal for the unit inverter 421, with a phase difference of, for example, 30° between them. When a 30° phase difference is added to the control signal, the voltage ripple of the 6fi component becomes a 180° phase difference between both inverters, canceling each other out, and no ripple voltage occurs in the composite input voltage e. Note that the ripple reduction amount is maximum at 30', but if an appropriate value is selected, the ripple voltage can be reduced accordingly.

By the way, when a DC electric vehicle is driven by series-connected inverters, the diameters of the wheels connected to each unit inverter are usually different from each other. Therefore, even if the inverter is started with a phase difference in the control signal as described above, this phase difference will also change over time. FIG. 2 shows this situation, and shows an example in which the signals are started at the same phase. This is an example in which even if the inverters start with the same phase when 1=0, a shift occurs in the inverter frequency due to the wheel diameter difference, and here a phase difference of Δθ occurs at t=T. Therefore, the countermeasure method will be explained below.

FIG. 3 is a schematic diagram of the DC electric vehicle system.

In the same figure, 100 is a train with four wheels 811.81
2,821,822. Wheel 811 is driven by electric motor 711, and similarly wheel 812 is driven by 712.821.
721 and 822 are driven by 722, respectively. 6
is an inverter system containing unit inverters that drive four electric motors. Wheels and electric motor are train 1
It is attached to carts 91 and 92, which are divided into two groups, before and after 00. Note that the diameter of wheels within the same bogie is usually controlled more strictly than between the bogies.

FIG. 4 shows a specific example of the inverter system shown in FIG. 3.

In the figure, 611, 612, 621, and 622 are unit inverters, and 613, 614, 623, and 624 are input capacitors. Here, the inverters 611 and 612 that drive the electric motor in the same truck are operated with a phase difference that can cancel the ripple voltage, and the inverters 621 and 622 are also operated with a predetermined phase difference. drive.

Therefore, if the difference in wheel diameter within the same truck is small, the phase difference shift when the inverter frequency is near 8 Hz will be small and will not pose a major problem. On the other hand, if the wheel diameter difference becomes a problem, adding a wheel diameter correction function will solve this problem.

Note that although the above example uses a voltage-type PWM inverter as the voltage-type inverter, the present invention can be similarly applied to a voltage-type square wave inverter.

Moreover, although the case where the present invention is mainly applied to a DC electric vehicle system has been described above, the present invention can be applied to general systems similar to this.

[Effects of the Invention] According to the present invention, phase difference operation is performed between the inverters connected in series, so that: 1) The combined voltage ripple of the input capacitor of the inverter is reduced.

11) Since the voltage ripple is reduced, the inductance of the input filter reactor can be reduced.

ij) Harmonic currents flowing through overhead contact lines and track circuits are reduced.

Benefits such as:

[Brief explanation of the drawing]

Fig. 1 is a time chart for explaining the present invention in detail, Fig. 2 is a waveform chart for explaining the wheel diameter error of a train,
Fig. 3 is a schematic diagram showing a DC electric vehicle system, Fig. 4 is a block diagram showing a specific example of the inverter system shown in Fig. 3,
FIG. 5 is a schematic diagram showing the proposed method, and FIG. 6 is a waveform diagram for explaining its operation. Symbol explanation 1... Electric contact line, 2... Rail, 3... Input filter reactor, 6... Inverter system, 41.4
2... Inverter unit, 51, 52, 711-7
22...Electric motor, 91.92...Dolly, 100...
・Train, 411.421,611~622...Unit inverter, 412,422,613~624...
Input capacitors, 811-822...wheels. Agent Patent Attorney Akio Namiki No. 1 Prisoner d @2 Figure 3 Figure 4 Figure 2 Rail Kuzu 5 Figure 2 Shi-ru%6 Figure

Claims (1)

[Scope of Claims] 1) For a voltage-type VVVF inverter formed by connecting two or more voltage-type unit inverters in series on their DC input sides, each pair of voltage-type unit inverters that are individually controlled to drive a load, A method for controlling a voltage type VVVF inverter, characterized in that control signals for controlling each unit inverter constituting the unit are controlled by giving a phase difference to each other. 2) The method for controlling a voltage source VVVF inverter according to claim 1, wherein the phase difference is a phase difference that can reduce a frequency component six times as high as the fundamental frequency on the input side of the unit inverter.