JPH03183390A - Pwm control method for inverter - Google Patents

Abstract

PURPOSE:To minimize higher harmonics through simple structure by controlling the output voltage of an inverter through time synthesis of three output voltage vectors which are proximate to a voltage command vector. CONSTITUTION:Speed control and vector control operations are carried out through a speed detector 3, a speed regulator 4, a slip frequency operating unit 5, a phase command operating unit 6, a current detector 7, a current component detector 8, a q-axis current regulator 9 and a d-axis current regulator 10. Space vector control sections 13-16 perform time synthesis of output voltage vectors thus controlling the output voltage. In other words, three output voltage vectors proximate to an output voltage command vector are selected from detected rotary coordinate components of output current and output voltage/ output phase commands corresponding to the difference between thus detected components and their current command values. Since an inverter is controlled through selection based on the polarity of differential output current, higher harmonics can be minimized through a simple structure.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides
Regarding WM control method.

[Conventional technology]

As the performance of vector-controlled PWM inverters increases, there is an increasing demand for reducing output harmonics. A space vector PWM control method has been proposed as a harmonic reduction method, but conventionally, vector control calculations and PWM control have been treated completely separately, and the information on the vector control side is
It was not used effectively on the WM control side, and the necessary signals were calculated anew on the PWM control side, making the PWM calculation complicated. A method using information in vector control calculations has also been proposed, but if the magnetic flux calculated on the vector control side has a phase mismatch with the actual magnetic flux of the motor,
An appropriate output voltage vector cannot be selected, harmonics increase, and the objective cannot be achieved.

For this kind of content, for example, see Material 5 of the Institute of Electrical Engineers of Japan Research Group.
PC-87-55, IEA-87-13ppH~20
and Electrical Engineering B, Vol. 106, No. 2, pp. 89-96 (Sho 6l.
-2).

[Problem to be solved by the invention]

An object of the present invention is to provide a PWM control method that has a simple control configuration and can control harmonics to a minimum. Another object of the present invention is to provide a PWM control method that can prevent a reduction in neutral point current that is harmful to operation in a neutral point clamp type inverter in which each phase output voltage is controlled to three values.

[Means to solve the problem]

In order to achieve the above object, the rotating magnetic field coordinate component 11d+11q of the inverter output current (motor current) is detected,
Based on the output voltage command and output phase command calculated according to the deviation from the command value, three output voltage vectors close to the output voltage command vector are selected, and furthermore, they are selected according to the polarity of the output current deviation. One of these is selected to control the inverter output voltage.

In addition, in order to achieve the other object mentioned above, the neutral point current is detected, and the output voltage vector is
The mode that brings the neutral point current closer to zero is selected from the two switching modes, and the neutral point current is controlled to be reduced.

(Function) Since the output voltage command is calculated according to the deviation between the detected value of the rotational coordinate component of the output current and its command value, the required voltage command value is always calculated according to the output current. Since the inverter output voltage is controlled according to the temporal synthesis of three output voltage vectors close to the vector, the inverter output voltage can be controlled to a minimum harmonic according to the voltage command.The output voltage vector is selected according to the required voltage command value. Therefore, unlike the conventional method, errors in selecting the output voltage vector do not occur, and an increase in harmonics and loss of control can be prevented.

[Embodiment] The configuration and operation of an embodiment of the present invention will be described below. Figure 1 shows the configuration. 1 is an inverter whose output voltage is controlled by pulse width modulation control, 2 is an inverter■
3 is a speed detector that detects the rotational speed of the motor; 4 is a speed command ω- and a speed detection signal ω;
5 is a speed regulator that amplifies the deviation of and outputs a torque current command jl-, and 5 is a speed regulator that outputs a torque current command jl-, and 5 is a speed regulator that amplifies the deviation of the torque current command jl-.
Slip frequency calculator that outputs S*, 6 is 03 lines and ω
, 7 is a current detector that detects the output current, 8 is the detected current Using the θ wheel, i is the rotating magnetic field coordinate quantity i i
Current component detector that converts ll, i lq, 9 is 11
．． * and ilq are amplified, and the q-axis voltage command v xq *
10 is the excitation current command iId.
The deviation between the main voltage and the above 11d is amplified and the d-axis voltage command V1. a*
It is a d@current regulator that outputs.

Note that when calculating V1d* and vtq*, in order to prevent interference between the d-axis and the q-axis due to the induced electromotive force of the electric motor, each axis component of the induced electromotive force is calculated by a non-interference control section (not shown). It is added to the output of each current regulator. 11 is a phase calculator that calculates the phase angle γ of the voltage command vector based on vld*, v1'+*, and 0; 12 is a phase calculator that calculates five three-phase output current commands from l1d*, 11q'' 13 is a region determining means for determining the region where V* exists based on the phase angle γ of voltage command vector V*; 14 is a region determining means for determining a region where V* exists based on the phase angle γ of voltage command vector V*; Output current deviation calculation means, 15
is a voltage vector selection means for selecting a voltage vector that reduces the current deviation from the three voltage vectors selected by the region discrimination means 13 according to a signal from the calculation means ↓4;
Reference numeral 16 denotes a switching mode selection means for determining a switching mode having the minimum number of switchings in accordance with the selected voltage vector.

Next, we will discuss the operation. In numbers 3 to ↑O, speed control and vector control calculations are performed. i sq*
iiq and torque are controlled according to the rotational speed ωr
is ω' controlled to match the book.

At this time, vld*, Vl, q cars are ila, ilq
Since it is controlled according to the deviation between and its command, ixa,
V1+i* required to control ll'l according to the command value,
Vl- is calculated. This includes the effects of changes in motor magnetic flux (emf), leakage impedance drop, etc., so that the required voltage is always calculated.

Regarding the above operation, please refer to the 1986 IEEJ Industrial Application Division National Conference Nα70. Since the content of the relationship is described in pp. 319 to 324, detailed explanation will be omitted here.

Next, the space vector control units 13 to 16 will be described.

FIG. 2 shows a vector diagram regarding the output voltage command vector V*. The d and q axes are rotating coordinate axes that rotate at an angular frequency ωl, and the α axis is a U-phase axis.

V books are expressed by the following formula.

v*= vl, *"+vryu5choEJy・-(1)π Here, γ = θ*+-+δ δ* =-tan-'(vtll*/vtq*) By the way, each phase output of the inverter The voltage is + when the P-side element is on, and - when the N-side element is on. Therefore, for each phase as a whole, there are switching modes shown in Figure 3. Corresponding to each, the output voltage vector vO ,V
1 to V8t and V7 are determined, and they are shown in a vector diagram as shown in FIG. 4.

Since the output voltage vector is discrete as shown,
The output voltage V is controlled by temporal synthesis of three output voltage vectors that correspond to the vertices of the triangle that includes the city V, that is, are close to V*. While V* is within one triangle, V is synthesized according to these three voltage vectors, but
During this time, one of them is selected depending on the polarity of the current deviation so that the current deviation approaches zero.

FIG. 4 is a diagram illustrating the operation of the current deviation calculation means 14. When the deviation Δj between one current command and one actual current for each phase exceeds a predetermined value ΔX, the means outputs a signal according to the polarity of the deviation. Regarding the three phases, signals A to F are output when the range is outside the hexagon shown.

That is, rA when Δxu>ΔX, rBJ when ΔiW, rBJ when ΔX, "C" when ΔIV>ΔX, "DJ" when Δ]u, "E" when ΔX,>ΔX, and "E" when Δiv<−ΔX. "F" In the voltage vector selection means 15, a voltage vector that brings the current deviation closer to zero from the voltage vector of 3''' is selected according to A-F. Next, the switching mode selection means 16 selects the mode with the minimum number of switching based on the front floor mote.In other words, since there are two zero voltage vectors, vo and Vl, the previous one is V1. ~vB and if you select the zero vector this time, if the previous time was Vl, VB, VF, then Vo
If the previous time was "21%w' 4 r v6, then Vl
Select.

As described above, the inverter output voltage is controlled according to the seven currents, and the current 111. As a result of controlling llq to a predetermined value, Vne (V1d*, V1-) takes into account the effects of induced electromotive force fluctuations, leakage impedance drop, etc., and the required voltage value is always calculated. . Since the output voltage is synthesized and controlled using three voltage vectors close to V*, the output voltage (fundamental wave component) is controlled according to the seven vectors, and harmonics can be controlled to a minimum.

FIG. 7 shows the configuration of a neutral point clamp type inverter to which the present invention is applied. 1 is an inverter in which each phase is composed of a series-connected circuit of transistors 1 to 4; 2 is an electric motor; 3 is a diode rectifier; 4 is a DC smoothing reactor;
5 and 6 are smoothing capacitors, 7 is a neutral point current detector, 8
is a filter. Inverter 1 has a voltage of 0 when transistors 1 and 2 are on in each phase - 0 when transistors 2 and 3 are on, and a voltage of 0 when transistors 1 and 2 are on;
If expressed as 101-, the switching mode will be as shown in FIG. There are output voltage vectors from 0 to 18 corresponding to each, and they are shown in FIG. In this embodiment, the speed control and vector control calculations are the same as in the previous embodiment, and the voltage commands v 111*, V 1q*
is calculated similarly.

The area of the voltage command vector V* is the same as in the above embodiment (non-multiplexed).
In this example, it was determined only by the phase angle γ, but in this embodiment (multiplex), as shown in FIG.
cannot be determined only by the phase angle γ, and 1v*1
need to be considered. FIG. 10 shows a method for determining regions based on γ and 1v*1. The figure corresponds to the angle (30 degrees) from the U-phase axis to the broken line shown in Figure 8, but since the area boundary pattern is repeated every 30 degrees at any other angle, the memory element is used. Teγ and IV*I
The area can be easily identified from As in the previous embodiment, three output voltage vectors are determined by region discrimination, one is selected from them according to the polarity of the current deviation, and the output voltage is controlled.

In a neutral point clamp type inverter, when each phase output voltage is zero (clamped to the neutral point voltage), the output current flows into the neutral point, and the neutral point current iN shown in FIG. 7 flows. i
Since s includes a low-order ripple component three times the output frequency, the neutral point voltage fluctuates and stable operation cannot be performed. In the present invention.

is is detected through a filter, and a switching mode is selected according to its polarity to prevent reduction of IN.

iN occurs at output electric vectors 13-18 (see FIG. 9). There are two switching modes in them. One is a mode in which iN increases, and the other is a mode in which iN decreases. The polarity of ih is related to the voltage vector and the output current phase. Corresponding to the region of the output current vector shown in FIG. 11, a mode in which iN increases and a mode in which is decreases are shown in FIGS. 12 and 13, respectively. From this, if the polarity of the detected amount is after filtering the neutral point current is positive, it is possible to prevent iN from decreasing by selecting the mode in Figure 13, and in the opposite case by selecting the mode in Figure 12. can. This operation can be performed as described above by adding iN and output current i to the switching mode selection means 16 shown in FIG. Note that iN flows into the DC smoothing capacitor C and causes voltage imbalance between both capacitors, so instead of detecting iN, the unbalanced voltage is detected,
The same effect can be obtained by selecting the switching mode in accordance with the polarity in the same manner as described above.

As described above, according to the present invention, the region of the voltage command vector in a neutral point clamp type inverter (series multiple inverter) can be easily determined.

Further, it is possible to prevent the neutral point current from being reduced which is harmful to the operation of the inverter. Note that the area determination can be similarly applied to a parallel multiplex inverter in which a plurality of unit inverters are connected in parallel using reactors.

〔Effect of the invention〕

According to the present invention, as explained above, the output voltage command is calculated according to the deviation between the rotating magnetic field coordinate component of the output current and its command value, and the temporal Since the inverter output voltage is controlled according to the synthesis, the output voltage can be controlled to minimize harmonics. Further, the region of the voltage command vector in the multiplex inverter can be easily determined based on the phase angle γ and the magnitude IV*1 of the vector. Furthermore, the neutral point current in a neutral point clamp type inverter is prevented from being reduced, and the inverter can be stably controlled.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of an embodiment of the present invention, Figures 2 to 6
7 is a diagram for explaining the operation, FIG. 7 is a circuit diagram of another embodiment of the present invention, and FIGS. 8 to 13 are diagrams for explaining the operation. DESCRIPTION OF SYMBOLS 1... Inverter, 13... Area determination means, 14.
...Current deviation calculation means, work 5...Voltage vector selection means, An #2 #3 Fig. #+口■ No. 1 Fig. 8 1) - Brown Fig. 9

Claims (1)

[Claims] 1. PW whose output voltage is controlled by pulse width modulation control
In the control method of the M inverter, the rotational coordinate component of the output current is detected, and from the output voltage command and output phase command obtained according to the deviation between the detected value and the current command value, the rotational coordinate component of the output current is determined to be close to the output voltage command vector. A PWM control method for an inverter, characterized in that three output voltage vectors are selected, and one of the three output voltage vectors is selected based on the polarity of the output current deviation to control the output voltage of the inverter. . 2. PW whose output voltage is controlled by pulse width modulation control
In the control method of the M inverter, the rotation coordinate component of the output current is detected, the output voltage command and the output phase command are determined according to the deviation between the detected value and the current command value, and the output voltage command and the output phase command are determine the phase angle of the output voltage command vector based on the phase angle, select three output voltage vectors close to the output voltage command vector based on the phase angle, and calculate the output current deviation from among the three selected output voltage vectors. A PWM control method for an inverter, characterized in that one is selected based on the polarity of the inverter to control the output voltage of the inverter. 3. In an inverter PWM control method in which the output voltage of each phase is controlled to three values of +E/2, 0, and -E/2, and the output voltage is controlled by pulse width modulation control, the rotational coordinate component of the output current is detecting, determining an output voltage command and an output phase command according to the deviation between the detected value and the current command value, and determining the magnitude and phase angle of the output voltage command vector based on the output voltage command and the output phase command, Three output voltage vectors close to the output voltage command vector are selected, and one of the three output voltage vectors is selected based on the polarity of the output current deviation to control the output voltage of the inverter. Characteristic PWM control method for inverters. 4. In the PWM control method of an inverter, where the output voltage of each phase is controlled to three values of +E/2, 0, and -E/2, and the output voltage is controlled by pulse width modulation control, the neutral point current is detected. A PWM control method for an inverter, characterized in that one of two switching modes having the same output voltage vector is selected depending on the polarity of the detected current, and control is performed so that the neutral point current approaches zero. 5. In the PWM control method of an inverter, where the output voltage of each phase is controlled to three values of +E/2, 0, and -E/2, and the output voltage is controlled by pulse width modulation control, the neutral point voltage is detected. , PWM control of an inverter, characterized in that one of two switching modes having the same output voltage vector is selected according to the polarity of variation in the detected voltage, and control is performed so that variation in the neutral point voltage approaches zero. Law.