JPH0412798Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a control circuit for a current-source three-phase inverter, and more particularly, to a control circuit that uses both a PWM method and a vector control method.

When operating an induction motor using a current-source three-phase inverter, basically three-phase alternating current is converted to direct current by a bridge rectifier circuit, and then this direct current is passed through a thyristor controlled by a signal from a speed setting device. The current source is converted into three-phase alternating current using a three-phase inverter, and the speed of the induction motor is controlled. In this case, the load current that is the output of the current source three-phase inverter becomes a rectangular wave with a phase difference of 120 degrees, but this rectangular wave current contains harmonic components, which causes pulsations in the torque of the induction motor. minutes arise.

The PWM method is a conventionally known method for removing this torque pulsation. this
An example of the PWM method is as follows. Divide the above-mentioned square wave current into, for example, 60°, and divide it into 0°
From 60° to 60°, the conduction width of a given thyristor (the pulse width of the conduction width pulse on the waveform) is gradually widened, and the pulse interval is gradually narrowed, and from 60° to 120°.
From 120° to 180°, the pulse width is gradually narrowed and the pulse interval is gradually widened using another combination of thyristors in the current source three-phase inverter. It is a control method. In other words, the pulsed load current generated by the conduction width of the thyristor is approximated to a sine wave to suppress harmonic components.

On the other hand, a vector control method has also been proposed for current-source three-phase inverters, which improves responsiveness by controlling the phases of the three-phase load currents ( _a , _b , and _c ). This method is as follows. When considering the load current waveform of the above PWM method, one load current (for example, _a ) is taken per cycle. In this case, from 0° in a half cycle of positive polarity
Mode up to 60°, mode from 60° to 120°,
120° to 180° mode, 180° to 240° mode with negative polarity half cycle, 240° to 300°
mode, can be divided into modes from 300° to 360°. If the set speed of the induction motor is changed based on this PWM method, the load current will increase or decrease.
The phase difference between the load current and the magnetic flux of the induction motor changes depending on the magnitude of the load current. In order to improve the response at this point, the thyristor conduction combination of the current source three-phase inverter is changed from mode to mode at the time of change, for example. In other words, the thyristor is forced to undergo commutation correction. In this way, PWM
The system suppresses torque pulsation and the vector control system improves quick response.

However, vector control has the following drawbacks. In other words, for commutation correction, it is necessary to calculate the phase difference between the current waveform at the time of the change and the corrected waveform, but conventional methods calculate the current phase at the time of each output of each waveform. Because of this, the calculations and other controls had become extremely complex.

Therefore, in view of the above-mentioned drawbacks, the present invention
The purpose of this paper is to provide a control circuit for a current-source three-phase inverter that simplifies the current phase calculation and has good characteristics, assuming the adoption of the PWM method and vector control method.

The present invention achieves this objective by controlling the speed of an induction motor using vector control using a current-source three-phase inverter using a PWM control method. In a control device for a current-source three-phase inverter that calculates the phase difference between the firing pulses of the thyristor elements in order to forcibly correct the commutation of the thyristor elements, which are switching elements of the inverter, and perform follow-up control, When the current phase is delayed by sequentially assigning a number n from 0 to 9 to each significant state of the PWM waveform (indicating whether it is a conduction pulse state or a state between conduction pulses of the PWM waveform), When n = 0, the phase angle is widened by the amount of delay and when the current phase is advanced, the significant state number n on the PWM waveform is determined in accordance with the phase change, and if n is an odd number, the current is caused to flow one revolution. , when n is an even number, in order to prevent commutation, pulses are generated at the rise and fall of the primary current in order to detect the phase difference between the magnetic flux of the induction motor and the primary current, and the interval α between these pulses is an α control circuit that controls the α value, a Δφ calculation circuit that calculates the phase angle Δφ between the excitation current and the primary current based on the α value of this α control circuit, and a Δφ calculation circuit that stores the value of this Δφ and the value in memory in advance.
Phase angle _θ from the reference point of the PWM waveform to the rise and fall of the pulse of the PWM waveform divided into 60 degrees
A commutation _No. determination circuit that calculates the significant state number n of the PWM waveform such that θ _o +Δφ>0 from ~θ _n , the pulse width of the PWM waveform, and the phase angle between pulses α ₀ ~ α n, and θ _o An α _N calculation circuit that calculates +Δφ=α _N , a circuit that calculates the time α _N /W ₀ by dividing α _N by the angular frequency W ₀ , and generates a pulse based on this α _N /W ₀ time. The present invention is characterized by comprising a pulse generation circuit and a ring counter for distributing this pulse signal to the gates of the thyristor elements.

Here, the principle and embodiments of the present invention will be explained with reference to the drawings. The commutation correction according to the present invention is performed in a waveform section in which the conduction width pulse gradually increases, for example, from 0° to 60° (i.e., π/3). Figure 1 shows the case of four conduction width pulses with a PWM waveform from 0° to 60°. That is, from 300° for convenience
The rising edge of this pulse (360° or
0°) to 60° is divided into nine sections. These nine sections are each numbered, and among 0 to 8, the four odd numbers 1, 3, 5, and 7 indicate the pulse width of the conduction width pulse, and 0, 2, 4, 6, and 8 indicate the pulse interval. show. The determination of this number is such that, for example, 0 or an even number indicates conduction of thyristors 1 and 2 shown in FIG. 5, and an odd number indicates conduction of thyristors 3 and 2. Then, phases α ₀ to α ₈ are determined corresponding to each number section on the PWM waveform, that is, corresponding to each significant state of the pulse interval and pulse width.

Further, the phases θ ₀ to _{θ 8} are determined from the aforementioned reference point corresponding to 0° corresponding to the PWM waveform. For this reason,
As clearly shown in Figure 1, θ ₀ = α ₀ , θ ₁ = α ₀ +
α ₁ , θ ₂ = α ₀ + α ₁ + α ₂ , θ ₃ = α ₀ + α ₁ + α ₂ + α ₃ …
A relationship exists. That is, the relationship θ _o = _N 〓 ^K=0 α _K holds true.

Based on the PWM waveform shown in FIG. 1 described above, when the load current changes, the current phase must be changed using a vector control method. FIG. 2 shows a case where the motor current decreases and the current phase is delayed. That is, in FIG. 2, the delayed phase angle Δψ is calculated in response to the current decrease, and from the phase angle θ ₀ stored in advance by determining this phase angle, α _N =θ ₀ +
A calculation of Δψ is performed. This α _N is the phase of θ ₀ including the delay angle, and is substantially the same as when θ ₀ is widened by Δψ.

Next, FIG. 3 shows a case where the conduction thyristor of the current source three-phase inverter is not changed based on the phase angle when the motor current increases and the current phase is advanced. In the same figure, the leading phase angle Δψ is calculated in response to the increase in current, and this Δψ is substituted into θ _o +Δψ, and θ _o
Determine n when +Δψ>0. In this case, Δφ
is a + sign in the case of a delay, and a - sign in the case of a lead. When n is determined by this calculation, for example, n
In the case of =2 (an even number), the thyristors 1 and 2 shown in FIG. 5 remain conductive. In this case, of course, no commutation takes place. Furthermore, n
After determining α _N =θ _o +Δψ is calculated and number 2
Determine how much phase remains until the next commutation based on the reference point. As a result, the advance angle of the current phase becomes clear, and the trigger generating section for controlling the inverter can be controlled according to this angle.

FIG. 4 shows a case where the motor current increases and the current phase is advanced, and the conduction thyristor of the current source three-phase inverter is commutated based on the phase angle. In _this case as well, n
seek. In FIG. 4, n=3, but in this case thyristors 3 and 2 are rendered conductive and commutation is performed. Also, as in the case of Fig. 3, θ _o +Δψ=α _N
is calculated to determine how far the state n=3 is from the reference point. As a result, the leading angle of the current phase becomes clear.

In this way, the current phase is changed only when delay and lead are n = 0, and n
=0, it is sufficient to determine α _N according to a predetermined pattern.

FIG. 6 is a block diagram for performing each of the above calculations. In the figure, 10 is an α control circuit that generates pulses at the rise and fall of the primary current to generate a phase difference between the exciting current, that is, the magnetic flux, and the primary current, and controls the interval α between these pulses; 11 12 is a Δψ calculation circuit that calculates Δψ using the excitation current and the primary current based on the α value of the α control circuit, and 12 is a Δψ calculation circuit that calculates Δψ using the value of Δψ and θ ₀ to θ _n stored in advance in the memory 13 to calculate θ _o +Δψ>0. Commutation NO to calculate n
14 is an α _N calculating circuit for calculating α _N =θ _o +Δψ; 15 is a circuit for calculating time α _N /ω ₀ by dividing α _N by the angular frequency; and 16 is a pulse that generates a pulse based on this time. The generating circuit 17 is a ring counter. The commutation correction is determined by the even or odd number of n in the commutation NO determining circuit 12, and the ring counter 17 is controlled, and the commutation time is set by a pulse of time α _N /ω ₀ . Furthermore, if the output of the Δψ calculation circuit 11 is a + sign, it means that the delay is delayed, so the output of Δψ can be directly input to the α _N calculation circuit 14.

As explained in the embodiments above, according to the present invention, when delaying the current phase, θ ₀ is made wider by Δψ,
When advancing, find n from the formula θ _o + Δψ > 0, and if n is an odd number, there will be one commutation, and if it is an even number, there will be no commutation.
without calculating the current phase for each waveform.
Calculations can be simplified.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram showing an example of a PWM waveform, Figure 2 is a waveform diagram showing an example of a PWM waveform.
The figure is a correlation waveform diagram when the current phase is delayed.
The figure shows a correlation waveform diagram in which the current phase is advanced and commutation correction is not performed, Figure 4 is a correlation waveform diagram in which the current phase is advanced and commutation compensation is performed, and Figure 5 is an inverter circuit that is an example of a current source three-phase inverter. FIG. 6 is a block diagram showing one embodiment of the present invention. In the drawing, 12 is a commutation NO determination circuit, and 14 is an α _N calculation circuit.

Claims (1)

[Scope of utility model registration request] When controlling the speed of an induction motor using vector control using a PWM control type current source three-phase inverter, the set speed of the motor is changed and the phase difference between the load current and the motor's magnetic flux is changed to a thyristor element, which is a switching element of the inverter. In a current-source three-phase inverter control device that calculates the phase difference between the firing pulses of the thyristor elements, in order to forcibly correct the commutation of the thyristor element and perform follow-up control, the phase difference between the magnetic flux of the induction motor and the primary current is detected. an α control circuit that generates pulses at the rise and fall of the primary current and controls the interval α between the pulses;
A Δφ calculation circuit that calculates the phase angle Δφ between the excitation current and the primary current based on the α value of the control circuit, and a PWM that is divided into 60 degrees from the reference point of the PWM waveform stored in memory in advance and the value of this Δφ. The phase angle between the rising and falling pulses of the waveform θ _p ~ θ _n and the phase angle of the pulse width and interval between pulses of the PWM waveform α _p ~
A commutation No. determination circuit that calculates the significant state number n of the PWM waveform such that θ _o +Δφ>0 from α _n , and θ _o +Δφ
= α _N calculation circuit for calculating α _N , a circuit for calculating time α _N /W ₀ by dividing α _N by angular frequency W ₀ , and this α _N /
A control circuit for a current-source three-phase inverter, comprising a pulse generation circuit that generates a pulse based on the time of W ₀ and a ring counter that distributes this pulse signal to the gate of the thyristor element.