JPS60229673A - Inverter - Google Patents

Abstract

PURPOSE:To improve the general efficiency of an inverter drive motor by switching to a double voltage rectifier at a high load time and to a full-wave rectifier at a low load time. CONSTITUTION:When a power source is single phase 100V, a contact 11 is contacted at A, and when a contact 12 is closed, a double voltage rectification is executed so that a DC voltage becomes 282V. On the other hand, when the contact 11 is contacted at B and the contact 12 is OFF, all voltage full-wave rectification is executed so that the DC voltage becomes 141V. The contacts 11, 12 are switched when the duty of a transistor 3 is, for example, detected or the voltage of a connection cable 6 is detected to index necessary DC voltage so that a necessary DC voltage becomes 141V or lower, and switched from the double voltage rectification to all-voltage rectification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inverter for motor coupling, and is concerned with improving the overall efficiency of an inverter-driven motor.

[Background of the invention]

FIG. 1 is a circuit diagram of a conventional inverter. 1 is a rectifier diode bridge, which together with 2 smoothing capacitors forms a rectifier circuit. When the power source is single phase 100V, a voltage doubler circuit is used to reduce the current of the motor 4. 3 is a transistor, and these 6 transistors are controlled by 5 control circuits to generate 3-phase alternating current and operate 4 motors. FIG. 2 shows the voltage waveforms of the 6-connection cable portion of FIG. 1. 7 is a main frequency waveform, and 8 is a chopping waveform for voltage adjustment. That is, the rotation speed is adjusted using this basic frequency, and the torque is adjusted using the chopping duty.

Figure 3 shows the total efficiency, which takes into account each rotation speed, inverter efficiency, and motor efficiency when the rotation speed at full speed is taken as a factor of 100.
This is an example of a DC brushless motor.

When the duty falls and the rotational speed is low, the waveform becomes a distorted wave as shown in FIG. 2, and as the duty falls, the waveform rate increases. Therefore, not only the chopping efficiency of the three transistors decreases, but also the copper loss of the motor increases, and as the rotational speed decreases as shown in FIG. 3, the efficiency decreases rapidly.

[Purpose of the invention]

The present invention aims to prevent this decrease and improve the overall efficiency in the low rotation range, as shown in FIG. 3, 10.

[Summary of the invention]

In other words, when the duty drops in the low rotation range, the rectifier circuit is switched from voltage doubler rectification to full voltage full wave rectification, increasing the duty and lowering the waveform factor to reduce loss and improve efficiency. .

[Embodiments of the invention]

An embodiment of the invention is shown in FIG. Components common to those in FIG. 1 are given the same reference numerals. 11 and 12 are relay contacts.

When the power supply is single phase 100V, contact 11 and A112 are ON.
In this case, voltage doubler rectification is performed and the DC voltage becomes 282V. On the other hand, when B112 of B11 is OFF, all voltages are full-wave rectified, and the DC voltage becomes 141V. The present invention is applicable whether the motor 4 is an AC induction motor or a DC brushless motor.

Contacts 11 and 12 determine the necessary DC voltage by, for example, detecting the duty of the three transistors or detecting the voltage of the connection cable 6, and switch when the required DC voltage becomes 141 V or less, and double the voltage. Switch to full voltage rectification.

The timing of this switching is not limited to 141v,
It should be determined appropriately. Since the main focus of the present invention is to appropriately switch between the voltage doubler and the total voltage, the inside of the control circuit 5 will not be described in detail, but the use of a microcomputer,
Furthermore, it is possible to easily construct a switching circuit even in a discrete circuit without using a microcomputer.

During switching, the most difficult control is torque control. Assuming that the rotational speed is constant, the fundamental frequency does not change, so it is necessary to control the duty approximately twice. This requires the application of a microcomputer, but if it is difficult to realize for the time being, even if it is temporarily stopped and restarted, it is fully practical when applied to, for example, a room near conditioner.

According to the present invention, as shown in FIG. 3, it is possible to increase the voltage duty when the rotation speed ratio is about 50 or less, thereby increasing the overall efficiency. Energy-saving operation, which is the original purpose of an inverter, is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional inverter, FIG. 2 is a voltage waveform, FIG. 3 is a motor overall efficiency, and FIG. 4 is a circuit diagram of an inverter to which the present invention is applied. DESCRIPTION OF SYMBOLS 1... Diode bridge, 2... Smoothing capacitor, 3... Transistor, 4... Motor, 5... Control circuit, 11... Contact, 12... Contact. Agent Attorney: Meiho Takahashi 1 Mouth↑

Claims (1)

[Claims] 1. An inverter with a circuit that uses a voltage doubler rectifier circuit when the load is high and switches to a full-wave rectifier circuit when the load is low.