JP3286046B2 - Power converter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pulse width modulation control (P
Output voltage by the WM control) is relates to the control how the power conversion device, such as a chopper or inverter which is controlled.

[0002]

2. Description of the Related Art FIG . 4 is a block diagram showing a conventional PWM inverter as a conventional power converter disclosed in Japanese Patent Publication No. 3-79959 . In FIG. A rectifier circuit 52, which is a power converter such as a PWM inverter which converts the direct current from the rectifier circuit 51 into an alternating current and supplies the alternating current to an AC motor 57 as a load, for example, a self-extinguishing type such as a transistor or a GTO thyristor. It is configured using switching elements.

An adder 61 adds an output of a carrier control circuit 53 and an output of a carrier center frequency setting circuit 60, 54 is a carrier signal generating circuit connected to the output side of the adder 61, and 55 is a carrier signal generating circuit. The output of the circuit 54 is compared with the output of the output voltage pattern generation circuit 56, and P
A comparator 58 that outputs a WM signal is a gate circuit that amplifies the PWM signal and supplies the amplified signal to the PWM inverter 52.

Next, the operation will be described. The rectifier bridge 51 converts AC from the three-phase AC power supply 59 into DC and supplies the DC to the power converter 52. The carrier control circuit 53 outputs a pattern signal such as a sine wave or a triangular wave for periodically changing the frequency of the carrier signal, and the carrier center frequency setting circuit 60 sets a constant signal (DC signal) for setting the center frequency of the carrier signal. ) Is output. Subsequently, these pattern signals and the center frequency setting signal are added by the adder 61 and input to the carrier signal generation circuit 54 as a carrier frequency command signal.

The carrier signal generating circuit 54 generates a carrier signal whose frequency is proportional to the amplitude of the carrier frequency command signal. Then, the comparator 55 compares the amplitude of the carrier signal with the amplitude of the control signal output from the output voltage pattern generation circuit 56, and uses the comparison result as a PWM signal having a pulse width determined by the pulse width modulation control. Output to the gate circuit 58. Subsequently, the gate circuit 58
Controls the power converter 52 by amplifying the PWM signal.

By the above-described PWM control operation, the power converter 52 outputs an AC voltage proportional to the output signal of the output voltage pattern generating circuit 56, and drives the AC motor 57. Here, the carrier control circuit 53 changes the frequency of the carrier signal output from the carrier signal generation circuit 54 with time. Therefore, the frequency of the harmonic component included in the output voltage of the PWM inverter 52 changes with time, and the harmonic having the same frequency is not applied to the AC motor 57 continuously. As a result, AC motor 57
The frequency distribution of the magnetic sound generated by the variance is distributed by changing the carrier frequency, that is, the frequency of the PWM signal with time. Therefore, the peak level of the magnetic sound is reduced, and the magnetic sound can be reduced.

[0007]

Since the conventional power converter is configured as described above, if the carrier frequency is largely changed in order to increase the effect of reducing magnetic noise, the carrier frequency will be reduced. The switching loss of the switching elements constituting the power converter increases in proportion. Therefore, there is a problem that heat is generated due to switching loss in a region where the carrier frequency is high.

At present, a microcomputer is often used for performing the PWM control. In this case, the PWM control is usually performed in synchronization with the carrier frequency. When the carrier frequency is changed with time, the carrier cycle, that is, the operation cycle of the PWM control is shortened in a region where the carrier frequency is high, so that there is a problem that the operation time is insufficient.

On the other hand, in the region where the carrier frequency is low, the problem of the calculation time does not occur, but the calculation period of the PWM control becomes longer, so that the update period of the voltage command becomes longer. As a result, there has been a problem that the ripple of the primary current supplied to the AC motor increases, and the torque ripple and harmonic loss of the AC motor increase.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems.
An object of the present invention is to provide a control method of a power conversion device capable of reducing a magnetic sound caused by a harmonic component by temporally changing a generation timing of an output voltage during one cycle of a carrier signal. And

[0011]

According to a first aspect of the present invention, there is provided a control method of a power conversion apparatus, wherein an average value of an output voltage during one cycle of a carrier signal is made to coincide with a voltage command and determined by pulse width modulation control. The generation timing of the output voltage is temporally changed without changing the pulse width.

According to a second aspect of the invention, there is provided a control method of a power conversion apparatus, wherein an average value of an output voltage during one cycle of a carrier signal is made to coincide with a voltage command, and a pulse width determined by pulse width modulation control is changed. Instead, one of the ON timing and the OFF timing of the switching element for obtaining the output voltage is temporally changed.

[0013]

According to a first aspect of the present invention, there is provided a control method of a power conversion apparatus, wherein an average value of an output voltage during one cycle of a carrier signal is made to coincide with a voltage command without changing a pulse width determined by pulse width modulation control. By changing the generation timing of the output voltage with time, harmonics of the same frequency are not continuously applied to the load, and generation of magnetic noise due to the harmonic components can be reduced.

According to a second aspect of the present invention, there is provided a control method of a power conversion apparatus, wherein an average value of an output voltage during one cycle of a carrier signal is made to coincide with a voltage command without changing a pulse width determined by pulse width modulation control. By changing one of the ON timing and the OFF timing of the switching element for obtaining the output voltage with time, the same effect as the first aspect can be obtained.

[0015]

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figure 1
FIG. 1 is a circuit diagram showing an embodiment of the invention according to claims 1 and 2 ;
, 1 is a step-down chopper circuit. In the step-down chopper circuit 1, a switching element 3 such as a transistor and a reactor 5 are connected in series between one terminal 8 of output terminals 7 and 8 and one terminal 9 of input terminals 9 and 10, and the output terminal 7 is connected. , 8, a cathode of a diode 4 is connected to a connection point between the switching element 3 and the reactor 5, and an anode of the diode is connected to an input terminal 1.
The DC power supply 2 is connected between the input terminals 9 and 10, and a load (not shown) such as a motor is connected between the output terminals 7 and 8. Therefore, the output voltage is supplied to the load when the switching element 3 is turned on and off.

Reference numeral 11 denotes switching signal generating means connected to the switching element 3, and is constituted by, for example, a delay circuit. 12 and 13 are switching signal generating means 11
Is a voltage command signal generating means connected to the comparator 12, and has a ROM 14a storing a V / F pattern, for example, and corresponds to a speed command signal F given from the outside. The output voltage command signal V ^* is output. Reference numeral 15 denotes a carrier signal generating means connected to the comparator 12 and the timing signal generating means 13. The carrier signal generating means 15 includes, for example, a crystal oscillator 15a and a counter 15b for counting an output signal of the crystal oscillator. The output signal of the counter 15b is directly clocked. And outputs it as a carrier signal a through a digital / analog (D / A) converter 15c.

[0017] Counter 1 the timing signal generating means 13 which inputs a clock synchronized with the falling edge of the carrier signal (sawtooth), counts the number of clock
6, when the count number is input as an address, the ROM 17 which outputs a timing signal t for changing the on-timing of the switching element 3 within the carrier cycle T by the delay time Td as a pattern signal such as a sine wave, a triangular wave, or random. It is configured.

Next, the operation of the first embodiment.
The DC power supply 2 applies a DC voltage between the input terminals 9 and 10 of the step-down chopper circuit 1. The carrier signal generator 15 outputs a carrier signal a (sawtooth wave) having a carrier cycle T and a clock signal synchronized with the falling edge of the carrier signal. Voltage command signal generating means 14 outputs voltage command signal V *.

The comparator 12 corresponds to on-time signal generating means. The comparator 12 receives a carrier signal a (sawtooth wave) having a carrier cycle T from the carrier signal generating means 15 and a voltage command signal V ^* from the voltage command signal generating means 14. By comparing the amplitudes of the two, as shown in FIG. 2, when the voltage command signal V ^* is larger than the carrier signal a, the on-time signal O, which is a binary signal of a low level, is switched to a switching signal. Output to the generating means 11. The on-time signal O is supplied to the switching element 3 constituting the step-down chopper circuit 1.
A signal proportional to the on time T _on in the carrier period T.

The switching signal generating means 11 receives the on-time signal O and the timing signal t output from the timing signal generating means 13, and converts the on-time signal O into a delay time Td by the timing signal t as shown in FIG. A switching signal s for driving the switching element 3 is generated and transmitted to the switching element 3 without delaying the pulse width determined by the pulse width modulation control. As a result, the step-down chopper circuit 1 of the output terminal 7 and the carrier signal a between 8 one period V as the average value between _{T out = T on / T ×} V in (= V *) ······ An output voltage that matches the voltage command signal V ^* of (1) is obtained.

[0021] Here, since the switching signal generating means 11 for time varying the timing signal t of the on-timing of the on-time signal O is output from the comparator 12, the timing signal generating means 13, the step-down chopper circuit 1
The harmonic component included in the output voltage of the above-mentioned voltage changes with time even if the carrier frequency is constant, so that harmonics of the same frequency do not continue.

[0022] In the above real施例, although either allowed one to temporally change the on-timing or off-timing of the switching elements in one period of the carrier signal, the on-off timing of the switching element Without changing, for example, a delay circuit is provided in a path for supplying the output of the switching element to the load, and the delay time of the delay circuit is changed to change the power supply timing to the load during one cycle of the carrier signal. Also, the same effects as in the above embodiment can be obtained.

[0023]

As described above, claims 1 and 2 are as described above.
According to the invention, the generation timing of the output voltage during one cycle of the carrier signal is temporally changed without changing the pulse width determined by the pulse width modulation control. Since either the on-time or the off-time of the switching element is changed with time in order to change, the harmonics of the same frequency are not continuously applied to the load, and the harmonic components are reduced. This has the effect of reducing the occurrence of magnetic noise caused by the noise. In addition, since the frequency of the carrier signal is not changed, there is an effect that heat generation due to switching loss in a high frequency region, shortage of operation time, or increase in ripple in a low frequency region can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a control device of a power conversion device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing operation waveforms of a comparator according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing operation waveforms of a switching signal generating means in Embodiment 1 of the present invention.

FIG. 4 is a configuration diagram showing a control device of a conventional power converter.

[Explanation of symbols]

 Reference Signs List 3 switching element 11 switching signal generating means 12 comparator (on-time signal generating means) 13 timing signal generating means 14 voltage command signal generating means 15 carrier signal generating means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-121065 (JP, A) JP-A-3-60376 (JP, A) JP-A-3-218265 (JP, A) JP-A-4-210 46568 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 7/48 H02M 3/155 H02P 7/63

Claims (2)

(57) [Claims] 1. A control method of a power conversion device for controlling an output voltage by pulse width modulation control, wherein an average value of the output voltage during one cycle of a carrier signal is made to coincide with a voltage command and determined by the pulse width modulation control. A method for controlling a power conversion device, characterized in that the generation timing of the output voltage is temporally changed without changing the applied pulse width. 2. A control method of a power conversion device for controlling an output voltage by pulse width modulation control, wherein an average value of the output voltage during one cycle of a carrier signal is made to coincide with a voltage command and determined by the pulse width modulation control. A method of controlling a power conversion device, characterized in that one of an on timing and an off timing of a switching element for obtaining the output voltage is temporally changed without changing a pulse width obtained.