JP2852083B2 - Inverter PWM control method and PWM inverter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a PWM control method in a PWM inverter.

[Conventional technology]

Recently, a method of reducing the magnetic noise of a PWM inverter drive motor by increasing the PWM frequency using an IGBT or FET has been put to practical use. However, the application is limited in that the inverter (cooling fin) becomes large and the cost increases because the element loss increases with the increase in the frequency.

[Problems to be solved by the invention]

An object of the present invention is to reduce magnetic noise by improving a PMW control method.

[Means for solving the problem]

In order to achieve the above object, the PWM inverter switching mode is changed with respect to its time arrangement or duration every predetermined period.

[Action]

By changing the time arrangement or duration of the switching mode at predetermined intervals, the phase of the harmonic current flowing through the motor winding changes periodically, thereby suppressing the vibration of the winding and its surrounding members, thereby reducing the magnetic field. Sound can be reduced.

〔Example〕

Hereinafter, the configuration and operation of one embodiment of the present invention will be described. FIG. 1 shows the configuration. 1 is an inverter whose output voltage is controlled by pulse width modulation control, 2 is a motor driven by the inverter 1, 3 is a driver for turning on and off a switching element of the inverter, 4 is a phase γ of the voltage command vector v ^* . The voltage vector quadrant discriminating means 5 for discriminating the quadrant in which v ^* exists on the basis of V ^* selects three output voltage vectors based on the signal from the quadrant discriminating means 4, and further selects the phase γ and magnitude | v of v ^{* *} | Is a voltage vector time arranging means for calculating the time distribution of each voltage vector based on |, 6 is a voltage vector time arranging means for determining the time arrangement of voltage vectors based on a signal from the quadrant discriminating means 4, and 7 is a time distribution. Switching mode selection means for selecting a switching mode (output voltage mode) based on signals from the means 5 and the time arranging means 6. Next, the operation will be described.

FIG. 2 shows a vector diagram relating to the inverter output voltage command v ^* . d and q axes rotating coordinate which rotates at the output angular frequency w _1, alpha axis shows the U-phase axis. v ^* is d and q
In synchronism with the shaft is a vector that rotates at w _1. The output voltage of each phase of the inverter is + when the P-side element is on, and − when the N-side element is on. Therefore, in each phase as a whole,
There are combinations (switching modes) shown in the figure. Output voltage vectors v ₀ , v _{1 to} v ₆ , v ₇ are determined for each of them, and these are shown in a vector diagram in FIG. Since the output voltage vector is the discrete value basis as shown, v To control the continuously output voltage v in accordance with ^* is, v ^* 3 one time of the output voltage vectors corresponding to the vertices of a triangle that forms the quadrant containing the V is synthesized by the appropriate blending. The above relationship is shown below using mathematical expressions.

The quadrant (I to VI) where the voltage command vector v ^* exists is determined by the quadrant determining means 4 according to the following equation.

The triangle occupying v ^* is determined by the above quadrant discrimination,
The three voltage vectors at that vertex are also determined. FIG. 9 shows three voltage vectors (zero vector v ₀ and v ₀₎ corresponding to each quadrant.
v ₇ is treated as the same vehicle). V ^* is synthesized using these output voltage vectors in each quadrant. _{^{That, v * = av n + bv}} n + 1 + cv 0,7 ...... (1) Here, n = 1 to 6, provided that when the _{n = 6 v n + 1 =} v 1 a, b, c: Time Allocation , a + b + c = 1 a, b, c is expressed by the following equation using the enclosure coordinate formula with reference to FIG.

Where Δ: total area of the triangle However, when n = 6 Δn + 1 = Δ1 Now, if | v _n | = | v _{n + 1} | = 1, in quadrant I, It is. The whole including the other quadrants is shown in FIG.
Every predetermined time T _s, divide the T _s a, b, a ratio of c, assigns each output voltage vectors corresponding to the divided periods. V Thus, the inverter output voltage in the average value of every T _s Time
Can be controlled to match ^* . As described above, the fundamental wave component of the inverter output voltage is controlled in accordance with v ^* . The calculation of a, b, and c is performed according to the time distribution method 5.

Next, the relationship between the harmonic components related to the magnetic sound and the time arrangement of the voltage vector will be described.

FIG. 5 shows the motor induced electromotive force as e and the output voltage vector.
v _n, a vector diagram showing the relationship v _{n + 1,} v _0,7. The harmonic current is generated in relation to the difference between each of v _n , v _{n + 1} , v _0,7 and e. The magnetic noise is generated by the excitation of the winding and its peripheral portion by the flow of the harmonic current through the motor winding, and the excitation force is proportional to the product of the harmonic current and the magnetic flux.

The exciting force acts on each part of the windings in a complicated manner. For simplicity, considering the exciting force components acting in the same circumferential direction on the stator or rotor of the motor, the components are harmonics parallel to e. It is proportional to the current vector component.

Incidentally, the time sequence of when to quenching mode selected at a predetermined time T _s (the output voltage vector) is conventionally illustrates in diagram a 6 (a). Here, when examining the change in the harmonic current component Δi parallel to e, when v ₀ and v ₇ are selected, Δi changes in the opposite direction to e, and v _n or v _{n + 1} If is selected. e in the same direction. FIG. 6 (b) shows the relationship. Because the time sequence of when to quenching mode is repeating give a time T _s as the period, the frequency of Δi is In other words, the excitation force is mainly composed of a component twice the switching frequency (about 2 kHz), so that the magnetic sound becomes extremely high and unpleasant.

Therefore, in the present invention, the vibration of the sound source, which is the source of the magnetic sound, is suppressed by changing the phase of the excitation force at predetermined intervals. FIG. 7 shows a time arrangement of the switching mode in that case. At this time, Δi changes as shown by the solid line in FIG. The change in the period T _{s1 and} the change in the period T _s2 have an opposite phase relationship with each other as shown by a broken line. In this way, the phase of the excitation force changes every predetermined cycle, and the above becomes possible.

In the case of the present invention, as shown in FIG. 7 (a), T _s1 ,
The arrangement and duration of the switching mode (voltage vector) are different in each period of T _s2 .

As described above, the time arrangement means 6 determines the time arrangement of the voltage vectors in the _Ts1 period and the _Ts2 period. For example, for the quadrant I, in the period T _s1 , v ₀ (1 unit) → v ₂ (1 unit) → v ₁ (1 unit) → v ₇ (1 unit) → v ₁ (1 unit) ) → v ₂ (1 unit) → v ₀ (1 unit) In the T _s2 period, v ₂ (1 unit) → v ₇ (2 units) → v ₁ (2 units) → v ₀ (2 units) → v ₂ (1 unit) The voltage vector array and its duration (unit time) are determined as _follows, and the total unit time of each of v ₂ , v ₁ and v ₀ , v ₇ is T _s1 and T _s2 . In the period, it is determined that Σtv ₂ = 2 units Σtv ₁ = 2 units Σtv _0,7 = 4 units, and these signals are sent to the switching mode selection means 7.

The selecting means 7 calculates the absolute value of each unit time from the following equation based on the signals from the time allocating means 5 and the time arranging means 6.

v ₁ unit time = a / total unit time v ₂ unit time = b / total unit time v _0,7 unit time = c / total unit time Based on the unit time absolute value, the time array The duration of the voltage vector is sequentially set in the timer according to the number of unit times, and the time arrangement of the voltage vector and its duration are controlled as shown in FIG. 7 (a). The relationship between the voltage vector and the switching mode is as shown in FIG. 8, and the ON / OFF state of each element of the inverter is controlled in accordance with the relationship.

The ratio of the sum of the respective durations of v ₀ , v _{n + 1} , v _n , and v ₇ is determined according to v ^*, and if v ^* is the same, it is constant in each period. That is, the fundamental wave component of the inverter output voltage is controlled according to v ^*, and does not fluctuate according to the periods of T _s1 and T _s2 . Therefore, even if the switching mode is changed as described above, no control problem occurs.
In this embodiment, each period is reported back as a set of the _Ts1 period and the _Ts2 period. However, each period is not limited to two types, and a plurality may be generally used. Further, the time of each period may be different. In this case, the frequency of the excitation force also changes, the noise changes to a soft sound, and the magnetic sound is reduced.

As described above, according to the present invention, there is an effect that the magnetic noise of the PWM control inverter drive motor can be reduced and mitigated.

[Effects of the Invention] According to the present invention, the switching mode in the PWM inverter is changed at predetermined intervals for the time arrangement or duration within the predetermined period, so that the phase of the harmonic current always changes. Thus, the magnetic noise can be reduced or reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG.
FIG. 10 is an explanatory diagram of the operation. 1... Inverter, 2... Voltage vector quadrant discriminating means,
5 ... voltage vector time distribution means, 6 ... voltage vector time arrangement means, 7 ... switching mode selection means.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-203869 (JP, A) JP-A-64-69266 (JP, A) JP-A-2-202396 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H02M 7/42-7/98 H02P 7/63

Claims (2)

(57) [Claims] In an inverter PWM control method in which an output voltage is controlled by pulse width modulation control, a time arrangement or a duration of a switching mode of an inverter selected according to an output voltage is changed at predetermined intervals. Inverter PWM control method characterized by the following. 2. An inverter for outputting a voltage when a switching element is turned on and off, and a switching mode is selected according to an output voltage of the inverter, and the switching element is turned on and off according to the selected switching mode. A PWM inverter comprising: means for turning off; and means for changing the time arrangement or duration of the switching mode at predetermined intervals.