JP2009303469A - Driving system of ac motor by single-phase electric power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain size reduction and cost reduction of a system, by eliminating a smoothing reactor from an AC motor drive circuit, using a single-phase power source and reducing the capacity of a smoothing capacitor. <P>SOLUTION: The AC motor 6 is connected to the output terminal of a three-phase inverter 5, and the neutral point of a stator winding in the AC motor is connected to one end of a single-phase power supply 1. The other end of the single-phase power supply 1 is connected to the connecting point of an anode in a first diode and a cathode in a second diode. Furthermore, the cathode in the first diode is connected to the positive terminal of the three-phase inverter, the anode of the second diode is connected to the negative terminal of the three-phase inverter, and a capacitor 4 is connected between the positive and the negative terminals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

Detailed Description of the Invention

Field of Invention

  The present invention relates to a power conversion system for a circuit that drives a three-phase AC motor (such as an induction motor or a permanent magnet synchronous motor) with a single-phase AC power source.

  FIG. 1 is a system that drives a three-phase AC motor by rectifying the output of a single-phase power source to obtain a DC voltage and using it as an input power source for a three-phase inverter. A single-phase power supply current is smoothed by a smoothing reactor, and a constant DC voltage is obtained by a smoothing capacitor.

Problems to be solved by the invention

  In the conventional AC motor drive device using a single-phase power source shown in FIG. 1, a device incorporated with a semiconductor element such as a diode or a three-phase inverter can be made compact. However, the smoothing reactor and the smoothing capacitor have a large capacity and a large volume. As a result, the equipment becomes larger and the cost increases.

  The present invention eliminates the reactor from the drive circuit by substituting the smoothing reactor with the leakage inductance of the AC motor, and reduces the capacity of the device by reducing the capacity of the smoothing capacitor for the purpose of improving the waveform of the single-phase power supply current. This is to reduce costs.

Means for Solving the Invention

  FIG. 2 shows a proposed driving apparatus for an AC motor using a single-phase power source. The proposed drive system consists of a three-phase inverter, a half-wave rectifier circuit, and a motor. One terminal of the single-phase AC power supply is directly connected to the neutral point of the stator winding of the motor, and the other terminal is a half-wave. Connect to the input terminal of the rectifier circuit. In the drive circuit for the AC motor shown in FIG. 2, the smoothing reactor and the two rectifier diodes are omitted, and the smoothing capacitor capacity is about two digits or more smaller than that of the conventional drive circuit shown in FIG.

The generated torque T of the AC motor driven by the non-sinusoidal three-phase PWM inverter is
T = T ₀ + T ₆ + T ₁₂ +...
Thus, in addition to the basic torque T _0, a harmonic torque having a frequency six times the inverter output fundamental frequency is generated. The main component of torque ripple is the sixth harmonic torque, and the higher order T ₁₂ +... Component is often negligible. The generation of the sixth harmonic torque is dominated by the voltage and current components of the fifth harmonic and the seventh harmonic. Therefore, the modified trapezoidal wave modulation signal shown in FIG. 3 is used as a drive signal for the three-phase inverter in the proposed circuit.

FIG. 3 shows a modified trapezoidal wave modulation signal in which a square wave is superimposed on a trapezoidal wave having a flat portion of 120 ° interval. e _b is a triangular wave carrier signal having an amplitude value E _b and an angular frequency ω _b , and e _u is a u-phase modified trapezoidal wave modulation signal having an amplitude value E _s and each frequency ω _s . γ is a square wave injection rate representing a ratio of injecting a square wave and has a value from 0 to 1. When γ = 0, a trapezoidal wave having a flat portion of a 120 ° section is obtained, and when γ = 1, a square wave having a 120 ° width is obtained. Become. In FIG. 4, E _u , E _v , and E _w are three-phase PWM signals obtained by a three-phase modified trapezoidal wave modulation signal and a triangular wave carrier signal, and E _uv is an inverter output line voltage waveform between the u phase and the v phase. . The square wave injection rate γ can greatly change the amplitude values of the fifth harmonic component and the seventh harmonic component included in the voltage waveform of the inverter output line, thereby suppressing the sixth harmonic torque and reducing the torque ripple. Reduction is possible. The amplitude of the fundamental wave component is substantially constant with respect to a large change in the value of γ, and the value becomes larger than that of the conventional sine wave modulation, so that the motor control range can be expanded.

  Furthermore, reducing the capacity of the smoothing capacitor improves the current waveform from the single-phase power supply. This is due to the characteristics of the modified trapezoidal wave modulation signal having a flat portion of 120 ° section. FIG. 5 is an example of a single-phase power supply current waveform with a smoothing capacitor of 1000 μF, and FIG. 6 is an example of a single-phase power supply current waveform when the smoothing capacitor capacity is 1 μF for improving the waveform. It can be seen that is obtained. Although the torque ripple is increased by reducing the capacitor capacity, the torque ripple can be reduced to the extent that there is no problem as a general power source for home appliances and the like.

The invention's effect

The conventional AC motor drive device using a single-phase power source has a large capacity and a large volume of the smoothing reactor and the smoothing capacitor, which increases the size of the device and increases the cost. In addition, it is necessary to improve the power supply current waveform, and many drive devices with a high power factor converter are found.
The present invention intends to realize a compact device and cost reduction with a circuit configuration in which a smoothing reactor is replaced with a leakage inductance of an AC motor to eliminate the reactor from the drive circuit and the capacity of the smoothing capacitor is reduced. . In order to make the best use of the proposed circuit, a modified trapezoidal wave modulation signal was applied, which enabled expansion of the control range, reduction of torque ripple, and improvement of the power supply current waveform. In particular, even if the smoothing capacitor capacity is reduced by 2 digits or more and the volume is reduced, a good power supply current waveform can be obtained. Therefore, there is a new possibility in terms of design, such as downsizing the entire device and incorporating a drive device in the motor. In the field of electric power application, many effects of the invention can be expected.

  A conventional AC motor drive device using a single-phase power supply.   Drive device for AC motor with proposed single phase power supply.   Modified trapezoidal wave modulation signal.   Generation of PWM pulses.   Single-phase power supply current waveform with a 1000 μF smoothing capacitor.   Single-phase power supply current waveform with 1 μF smoothing capacitor.

Explanation of symbols

1: Single-phase AC power source 2: Smoothing reactor 3: Full-wave rectifier circuit 4: Smoothing capacitor 5: Three-phase inverter 6: Three-phase AC motor 7: Half-wave rectifier circuit e _b : Triangular wave carrier signal E _b : Triangular wave carrier signal Amplitude e _u : u-phase modified trapezoidal wave modulation signal E _s : amplitude of modified trapezoidal wave modulation signal γ: square wave injection rate E _uv : inverter output line voltage E _u , E _v , E _w between u phase and v phase : Three-phase PWM signal obtained by three-phase modified trapezoidal wave modulation signal and triangular wave carrier signal

Claims (2)

  Connect the AC motor to the output terminal of the three-phase inverter, connect the midpoint of the stator winding of the AC motor to one end of the single-phase power supply, and connect the other end of the single-phase power supply to the cathode of the first diode and the second Connect the diode anode to the connected terminal. The anode of the first diode is connected to the positive terminal of the three-phase inverter. The cathode of the second diode is connected to the negative terminal of the three-phase inverter. Electric motor drive device. However, this includes the case where the capacitor is a snubber circuit.   The three-phase inverter in the drive unit shown in claim 1 is operated by a modified trapezoidal wave modulation signal in order to improve the current waveform of the single-phase power supply while reducing the capacitor capacity, and to reduce the motor torque ripple and the control range. Control method

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