JPH03190506A - Inverter circuit for ac electric vehicle - Google Patents

Abstract

PURPOSE:To reduce the size and the cost by connecting N units of VVVF transistor inverters in series and grounding the neutral point at which the inverters are separated in halves. CONSTITUTION:N(even number) units of VVVF inverters 6 are connected in series such that the DC intermediate circuit voltage can be made high. Since the voltage of the DC intermediate circuit increases when a plurality of inverters are connected in series, the intermediate point of series circuit of two inverters is grounded thus lowering the ground voltage. By such arrangement, the DC intermediate circuit voltage can be made high, output current of rectifier can be decreased correspondingly resulting in a low cost main rectifier having reduced size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter circuit for an AC electric vehicle that receives AC power from an overhead contact line, converts the power inside the vehicle, and drives an induction motor.

[Conventional technology]

Figure 2 shows a conventional example of an AC electric vehicle system.

In the figure, 1 is a pantograph, 2 is a main transformer, 3 is a main rectifier, 4 is a power/brake converter, 5 is a smoothing reactor, 6 is a transistor inverter, and 7 is an electric motor (induction motor).

In such a configuration, an extra high voltage is received from the overhead wire via the pantograph 1, and the voltage is stepped down within the vehicle by the main transformer 2. The stepped down voltage is rectified by the main rectifier 3 and converted into a DC voltage. Since the main rectifier 3 is usually divided into parts for harmonic countermeasures, the secondary side of the main transformer 2 is also divided according to the number of divisions of the main rectifier 3. The DC voltage controlled to be substantially constant by the main rectifier 3 is supplied to the inverter 6 through the P switch of the power/brake converter 4 and the smoothing reactor 5. The electric motor 7 connected to each shaft is individually operated at variable speed by an inverter 6 provided exclusively for the purpose. Therefore, as the inverter 6, variable voltage variable frequency (
V V V F) inverter is used. Note that during regenerative braking, the kinetic energy of the vehicle is transferred to the electric motor 7. Inverter 6, smoothing reactor 5. The power is regenerated through the converter B switch, main rectifier 3 (inverter operation), main transformer 2, and pantograph I.

That is, since the receiving voltage of AC electric cars is usually extra high voltage (20KV to 3OKV is common in Japan), a transformer 2 is installed inside the car and the DC intermediate circuit voltage (inverter input voltage) can be freely selected. and set the optimum value for the inverter 6. Also, invar.

In the evening, it is common for multiple units to be connected in parallel, and the number of parallel units is usually four (one inverter per each shaft load,
(4 sets per electric motor), transistor inverters are often used as inverters due to their cost.

[Section H that the invention attempts to solve] In the circuit configuration as described in Section 2, four inverters are connected in parallel, so each inverter has a current of l,
If a voltage of (1) is required, a current of 4I (voltage is V) must be supplied from the main rectifier 3, and a large-capacity and expensive one is required.

Particularly, when a transistor inverter is used as the inverter, the input voltage cannot be kept very high, so the increase in current becomes even more noticeable. Further, although the semiconductor elements constituting the main rectifier are used for large currents and usually have a high withstand voltage value, it cannot be said that the above-mentioned circuit configuration makes full use of the withstand voltage value of the elements.

Therefore, an object of the present invention is to reduce the burden on the main rectifier when driving an induction motor for driving a vehicle using a transistor inverter, and to enable the use of a small and inexpensive main rectifier.

[Means to solve the problem]

Converts alternating current from the overhead contact line into direct current (2, VVVF) and converts it into direct current (VVVF).

If N (even number) lunge inverters are connected in series in the DC intermediate circuit CJ of an AC electric vehicle that drives the AC electric vehicle at variable speed, the inverters in the series connected circuit are divided into N/2 inverters each. Ground the midpoint.

[Effect]

VVVF ) By connecting N range inverters in series, it is possible to obtain a high DC intermediate circuit voltage.
Therefore, the output current of the main rectifier can be made smaller accordingly, resulting in smaller size and lower cost.

〔Example〕

The feature of this invention is that the VVVF l-range inverter is connected to N (even number) so that the DC intermediate circuit voltage can be high.
The units are connected in series. However, when multiple inverters are connected in series, the voltage of the DC intermediate circuit increases, so here, for example, as shown in Figure 1, by grounding the intermediate point of each two series circuits, the ground potential is lowered. That's what I do. Note that FIG. 1 is a configuration diagram showing an embodiment of the present invention.

Here, two sets of inverters connected in series are connected in parallel, but all four inverters are connected in series,
The midpoint between dividing the inverter into two parts may be grounded. Generally, N inverters (an even number) are connected in series, and the midpoint between each dividing into N/2 inverters is grounded. is possible. In other words, by connecting an even number of inverters in series, it is possible to obtain a high DC intermediate circuit voltage, thereby reducing the main rectifier output current, and 1. By grounding the midpoint of each series circuit, 1. To lower the ground potential. It's another thing. In particular, in the embodiment shown in Fig. 1, there are 2
You only need to flow a current of I (voltage is ■), and if four are connected in series, you only need I (voltage is 4V or 2V).

Note that other points are the same as in Figure 2, so
Explanation will be omitted.

〔Effect of the invention〕

According to this invention, since the DC intermediate circuit voltage can be set high, the rectifier output current can be reduced correspondingly, and the main rectifier can be made smaller and cheaper than before. By grounding the point,
The ground voltage of the inverter can also be lowered, providing the advantage that the insulation level of the inverter can be lowered.

[Brief explanation of drawings]

FIG. 17 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is an intersection diagram. l! f This is a configuration 1a showing a conventional example of an electric medium system. Symbol explanation ■... Pantograph, 2... Main transformer, 3... Main rectifier, 4... Power running/braking converter, 5... Smoothing reactor, 6... Transistor inverter, 7...・Electric motor (induction motor), P, B...switch.

Claims (1)

[Claims] 1) In order to convert alternating current from the overhead contact line into direct current and drive a vehicle induction motor at variable speed via a VVVF transistor inverter, N (even number) VVVF transistor inverters are connected in series to the direct current intermediate circuit, and An inverter circuit for an AC electric vehicle, characterized in that an intermediate point of the series-connected circuit where the inverter is divided into N/2 inverters is grounded.