JPH0720396B2 - Inverter modulation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a modulation method of a VVVF inverter (inverter of variable voltage variable frequency) for driving an electric vehicle, for example, and particularly suppresses a motor current peak of a three-phase induction motor. The present invention relates to the inverter modulation method.

[Prior Art] FIG. 3 is a circuit diagram showing a main circuit configuration of a general VVVF inverter device for driving an electric vehicle.
0) supplies DC power to the VVVF inverter (25) via the pantograph (21), switch (22), reactor (23) and capacitor (24), and outputs AC voltage from the VVVF inverter (25). The voltage is applied to a three-phase induction motor (26) for driving an electric vehicle.

The normally closed switch (22) can appropriately disconnect the power supply to the VVVF inverter (25).
Further, the reactor (23) and the capacitor (24) form an inverted L-shaped filter, and the main circuit of the VVVF inverter (25) is a power semiconductor device (25u) to (25z) such as GTO.
It is composed by.

Next, the operation of the general VVVF inverter device shown in FIG. 3 will be described.

The DC voltage supplied from the overhead wire (20) through the pantograph (21) is supplied to the VVVF inverter (25) as a DC voltage Ed across the capacitor (24). The power semiconductor elements (25u) to (25z) in the VVVF inverter (25) are on / off controlled by a PWM signal from a control circuit (not shown), and generate an AC output voltage whose pulse width is modulated by VVVF. With this output voltage, three-phase induction motor (26)
Is driven at a predetermined rotation speed based on a driving command, and the electric vehicle can be accelerated / decelerated.

At this time, control the output voltage of the VVVF inverter (25)
The PWM signal is generated in the control circuit by comparing the modulated wave and the carrier wave. Also, carrier frequency f _CH
Changes according to the frequency of the output voltage, that is, the inverter frequency f _IN , and corresponds to P during one period of the inverter frequency f _IN.
If the pulse number of the WM signal is P, then f _CH = f _IN × P.

Next, a conventional inverter modulation method for obtaining such a PWM signal will be described.

4 to 7 show, for example, "IEEE IPEC-Tokyo'83 (Fig.
Pp. 1587 to pp. 1598) "," PW digitally controlled directly "
MGTO Inverter (DIRECT DIGITAL CONTROLLED PWM GT
O INVERTER) '' (especially on pages 1592 and 1594, Fig.
6 and FIGS. 8 to 10) are explanatory diagrams showing a conventional inverter modulation method. In this case, the carrier frequency
f _CH is changing in the synchronous mode with respect to the inverter frequency f _IN .

FIG. 4 shows PW generated based on carrier wave C and modulated wave M.
FIG. 6 is an explanatory diagram showing a basic operation for obtaining a pulsed output voltage Vo by an M signal. First, in the control circuit, the magnitudes of the triangular wave carrier C and the sine wave modulated wave M are compared, and a PWM signal having a pulse width τ corresponding to the section where C> M is continuously generated. The pulse width τ of the PWM signal changes depending on the magnitude of the modulation wave M, and the number of pulses P corresponding to one cycle of the inverter frequency f _IN changes depending on the frequency of the carrier wave C. With this PWM signal, power semiconductor device (25u)
~ (25z) is switched on and off, and VVVF inverter (2
The output voltage Vo of 5) is a pulse voltage that drops from the DC voltage level Ed to zero level only in the section of the pulse width τ. Therefore, the final output voltage Vo for the three-phase induction motor (26) is
Has a desired value according to the change of the pulse width τ of the PWM signal.

That is, the phase of the modulation wave M is determined so that the modulation wave frequency f _M matches the inverter frequency f _IN . At this time, the peak value A of the modulation wave M with respect to the peak value of the carrier C is A.
By changing (0 ≦ A ≦ 1), the pulse width τ of the PWM signal can be changed to change the effective value of the output voltage Vo. Further, the carrier frequency f _CH can determine the number P of pulses of the PWM signal in one cycle of the inverter frequency f _IN .

Fig. 5 shows the carrier frequency f _CH for the inverter frequency f _IN
FIG. 4 is an explanatory diagram showing a change of the DC voltage Ed in FIG.
The case of 00V is taken as an example. In the figure, the carrier frequency f _CH increases corresponding to the inverter frequency f _IN ,
With the increase of the inverter frequency f _IN, the number of pulses P for one cycle is gradually changed while switching sequentially to 51, 27, 15, 9, 5, 3 and finally, the non-pulse of the 1 pulse mode by energizing 120 ° The modulation state is set. In this case, carrier frequency f _CH
Is a synchronous mode for the inverter frequency f _IN ,
The number of pulses P is set to an odd number in order to change the pulse width τ of the PWM signal for one cycle of the inverter frequency f _IN . Also, since the pulse number P is switched stepwise,
The carrier frequency f _CH from the maximum value (about 550 Hz) at the time of switching is 30
It is rapidly decreasing to around 0Hz.

FIG. 6 is an explanatory diagram showing changes in the magnitude A of the modulated wave M with respect to the inverter frequency f _IN , in which the DC voltage Ed is 900 V, 15
The characteristic of the magnitude A of the modulated wave M when changed to 00V and 1900V is shown. In the figure, the magnitude A of the modulated wave M increases according to the inverter frequency f _IN , but the DC voltage Ed
Changes, the pulse voltage height of the output voltage Vo also changes, so the rate of increase of the magnitude A of the modulated wave M with respect to the inverter frequency f _IN changes. Therefore, the magnitude A of the modulated wave M
Is inversely proportional to the DC voltage Ed, and when the DC voltage Ed is low, it moves to the characteristic of the low side of the inverter frequency f _IN , and when the DC voltage Ed is high, it moves to the characteristic of the high side of the inverter frequency f _IN. ing. The state in which the magnitude A of the modulated wave M is 1.0 represents the non-modulated state in which the pulse number P is 1.

FIG. 7 is an explanatory diagram showing a motor current peak I _MP flowing in the three-phase induction motor (26) due to the modulation of the carrier frequency characteristic of FIG. In the figure, the maximum value is about 1050 A with respect to the fundamental wave motor current peak (about 650 A) shown by the one-dot chain line, and the fluctuation of the motor current peak I _MP is about 1.6 times.

Thus, when the fluctuation of the motor current peak I _MP is large,
Since an overcurrent flows through the power semiconductor elements (25u) to (25z), it is necessary to increase the capacity of the VVVF inverter (25). Also, if the carrier frequency f _CH is increased, the fluctuation of the motor current peak I _MP can be suppressed, but the power semiconductor element (2
The switching frequency of 5u) to (25z) increases and the heat loss increases. Therefore, a method of determining the carrier wave C in the asynchronous mode with respect to the phase of the inverter frequency f _IN and suppressing the ripple component of the motor current peak I _MP shown in FIG. 7 can be considered.

Next, a modulation method using the carrier frequency f _CH in the asynchronous mode will be described.

Figure 8 shows, for example, No. 17 in the collection of papers by the West German BBC "Electric Railway (Elektrische Bahnen)" (September-October 1979).
It is explanatory drawing which shows the modulation method by the asynchronous mode employ | adopted for West German Railways E120 described in the page. In the figure, the asynchronous carrier wave C with respect to the inverter frequency f _IN (that is, the modulated wave frequency f _M ) of 20 Hz or less has a constant cycle of about 190 Hz. In this case, the carrier frequency f _CH for the inverter frequency f _IN of 20 Hz or higher is
The phase of f _IN and the mode have been switched to the synchronous mode and are changing in stages. Therefore, for the inverter frequency f _{IN of} 20 Hz or higher, the motor current peak I _MP fluctuates as in FIG. 7.

[Problems to be Solved by the Invention] As described above, since the conventional inverter modulation method determines the carrier wave C in the synchronous mode with respect to the inverter frequency f _IN , the power semiconductor element in the VVVF inverter (25) is When the pulse number P of the PWM signal for controlling on / off of (25u) to (25z) is switched, the fluctuation of the motor current peak I _MP occurs, the torque fluctuation of the three-phase induction motor (26) occurs, and the inverter capacity There was a problem that it had to be increased. In the modulation method using the carrier wave C in the asynchronous mode as shown in FIG. 8, since the carrier wave frequency f _CH in the asynchronous region is constant at about 190 Hz, the control range of the inverter frequency f _IN is narrow (0 Hz to 20 Hz). For inverter frequency f _{IN of} 20Hz or more, there is a problem similar to the above, and there is a problem that the heat loss due to extra on / off switching of power semiconductor elements (25u) to (25z) cannot be ignored. It was

The present invention has been made to solve the above-described problems, and suppresses fluctuations in motor current peaks, reduces inverter capacity, and suppresses fluctuations in output torque of a three-phase induction motor, and An object of the present invention is to provide an inverter modulation method capable of suppressing heat loss by suppressing an on / off switching frequency of a power semiconductor element.

[Means for Solving the Problems] An inverter modulation method according to the present invention determines a carrier wave in an asynchronous mode with respect to the phase of the inverter frequency, and maximizes the carrier wave frequency when the amplitude of the modulated wave with respect to the carrier wave is near 0.5. In addition, the carrier frequency is continuously switched according to the inverter frequency and the output voltage.

[Operation] In the present invention, the carrier frequency is continuously increased in the asynchronous mode as the inverter frequency is increased, and the amplitude of the modulated wave with respect to the carrier is maximized in the vicinity of 0.5 and then decreased again. By doing so, the shock at the time of switching the pulse number of the PWM signal is suppressed and the carrier frequency is smoothly changed.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. First
FIG. 1 is an explanatory view showing an embodiment of the present invention, in which C, M,
A, f _CH and f _IN are the same as described above. FIG. 2 is an explanatory diagram showing the relationship between the carrier wave C and the modulated wave M and the output voltage Vo. The VVVF inverter device to which the present invention is applied is as shown in FIG.

Next, one embodiment of the present invention will be described with reference to FIGS.

In the low frequency region of the inverter frequency f _IN of 30 Hz or less, the carrier frequency f _CH determined in the asynchronous mode is changed from 100 Hz to 20 Hz as the inverter frequency f _IN increases.
Increase continuously up to 0Hz. At this time, the amplitude A of the modulated wave M with respect to the carrier increases from 0 to 0.5.
_CH becomes maximum. This is because the ripple rate of the motor current peak I _MP (see FIG. 7) becomes maximum in the vicinity of A = 0.5, and the carrier frequency f _CH at this time is maximized to suppress an increase in ripple.

That is, in FIG. 2, the modulated wave M and the carrier wave C when the inverter frequency f _IN is about 15 Hz are shown by solid lines, and the modulated wave M and the carrier wave C when the inverter frequency f _IN is about 30 Hz are shown by the one-dot chain line. The pulse interval of the output voltage Vo when the amplitude A of the modulated wave is around 0.5, as shown by the alternate long and short dash line, is the output at A ≈ 0.3 (see the solid line).
Adjusted more narrowly. Therefore, the ripple of the motor current peak I _MP can be reduced and controlled continuously. or,
At this time, the maximum value of the motor current peak I _MP is suppressed to about 950 A with respect to the fundamental wave motor current peak 650 A.

In the region where the inverter frequency f _IN is 30Hz-60Hz,
The carrier frequency f _CH determined in the asynchronous mode is continuously decreased. At this time, the amplitude magnitude A of the modulated wave M with respect to the carrier increases from 0.5 to 1.0.

The magnitude A of the modulated wave M is 1.0, that is, the inverter frequency f _IN
In the region where the pulse number P of the PWM signal in one cycle is 1, the carrier frequency f _CH increases in a one-to-one relationship with the inverter frequency f _IN .

Thus, in the asynchronous mode region, by continuously changing the carrier frequency f _{CH according} to the inverter frequency f _IN , the inverter frequency f _CH in the asynchronous mode is changed.
_{As the IN} control range increases, the motor current peak I _MP
It is possible to control continuously while suppressing the ripple component of, and it is possible to suppress the maximum value of the motor current peak I _MP . Further, since the carrier frequency f _CH can be suppressed and the on / off switching frequency of the power semiconductor elements (25u) to (25z) can be reduced, the inverter capacity and heat loss can be reduced.

As described above, according to the present invention, the carrier wave is determined in the asynchronous mode with respect to the phase of the inverter frequency, and the carrier wave frequency is maximized when the amplitude of the modulated wave with respect to the carrier wave is near 0.5. , The carrier frequency is continuously switched according to the inverter frequency and the output voltage, and the shock when switching the number of pulses of the PWM signal is suppressed to smoothly change the carrier frequency. And an on-off frequency of the semiconductor element can be reduced, torque fluctuations of the three-phase induction motor can be suppressed, and the capacity and heat loss of the VVVF inverter can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a carrier frequency characteristic according to an embodiment of the present invention, FIG. 2 is an explanatory view showing a change of an output voltage according to an embodiment of the present invention, and FIG. 3 is a general VVVF inverter device. FIG. 4 is a circuit diagram, FIG. 4 is an explanatory diagram showing a general process of generating an output voltage, FIGS. 5 and 6 are explanatory diagrams showing a conventional inverter modulation method using a carrier frequency in a synchronous mode, and FIG. Is an explanatory view showing a motor current peak by a conventional inverter modulation method, and FIG. 8 is an explanatory view showing a conventional inverter modulation method using a carrier frequency in an asynchronous mode. (25) …… VVVF inverter (25u) to (25z) …… Semiconductor element for power (26) …… Three-phase induction motor, Vo …… Output voltage M …… Modulated wave, C …… Carrier f _IN …… Inverter Frequency f _CH ...... Carrier frequency P ...... Pulse number of PWM signal A ...... Modulation wave size In the figures, the same symbols indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A modulation wave that uses a modulation wave that determines the magnitude of an output voltage from a VVVF inverter and an inverter frequency and a carrier wave that determines the number of pulses of a PWM signal corresponding to one cycle of the inverter frequency. And the carrier wave is compared to generate the PWM signal, and the VV is generated by the PWM signal.
In an inverter modulation method for controlling the output voltage applied to an induction motor by switching on and off of a power semiconductor element in a VF inverter, the carrier wave is determined in an asynchronous mode with respect to the phase of the inverter frequency, and the carrier wave An inverter modulation method, wherein the carrier frequency is maximized when the amplitude of the modulated wave is in the vicinity of 0.5, and the carrier frequency is continuously switched according to the inverter frequency and the output voltage.