JPH0221229B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a control method for a current-type three-phase inverter, and is useful for PWM control of the current-type three-phase inverter. FIG. 1 is a circuit diagram showing a current type three-phase inverter together with its control circuit and three-phase induction motor.
As shown in the figure, the current type three-phase inverter 1 includes six thyristors T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ and six commutation capacitors C ₁ , C ₂ , C _{3 .} , _C4 , _C5 , _C6
and diodes D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , and rectified DC by a three-phase bridge rectifier circuit 2 connected to a three-phase AC power supply (not shown). , and further converted back to alternating current to supply load currents i _a , i _b , and i _c , whose phases differ by 120° from each other, to the three-phase induction motor 3 . At this time, the ring counter 4 is
The voltage determined by the setting value of the speed setting device 5 is made to correspond to the frequency of the signal converted by the voltage/frequency converter 6, and the thyristors T ₁ to _{T 6} are sequentially triggered via the gate amplifier 7. The speed of the three-phase induction motor 3 is controlled by controlling the frequencies of the currents i _a , i _b , and i _c . As a result, the load currents i _a , i _b , and i _c which are the outputs of the current type three-phase inverter 1 become rectangular waves whose phases differ by 120 degrees, as shown in FIG. The output voltage control system of the three-phase bridge rectifier circuit 12 is composed of the operational amplifiers 8 and 9, the gate position adjuster 10, and the diodes 11 and 12 shown in FIG. However, in this technology, as mentioned above, the load currents i _a , i _b , i _c
Since it is a rectangular wave, harmonic components (particularly low-order harmonics such as the third harmonic and the fifth harmonic) are included, and this causes a pulsation component to be mixed into the torque of the three-phase induction motor 3. Therefore, a PWM control method has been proposed in order to eliminate the pulsation by making the waveforms of the load currents i _a , i _b , and _ic as close to sine waves as possible.
In this system, a PWM pattern generation section is provided in place of the ring counter 4, and the trigger timing of the thyristors _T1 to _T6 of the current type three-phase inverter 1 is controlled by the trigger pulse that is the output signal of this pattern generation section. be. More specifically, as shown in FIG. 3, for example, the thyristor _T6 is turned on during a 60° period (hereinafter referred to as the commutation period T) prior to the rise of the long pulse width period of the load current i _a . Thyristors T ₁ and T ₅ are turned on alternately, and thyristor T ₂ is turned on during a commutation period T of 60° after the rise of the long period of the pulse width of the load current _{i a} . By alternately turning on _T3 , a plurality of short pulses are formed before and after a long pulse width period. The shaded areas in FIG. 3 indicate that each of the thyristors T ₁ to _{T 6} is in a conductive state. Similar operations are performed for load currents i _b and i _c . In this way, the load currents _i a _-ic have a waveform as shown in FIG. 4, which is closer to a sine wave than a single rectangular wave. On the other hand, in the current type three-phase inverter 1,
A vector control method has also been proposed in which the phases of the load currents _{i a} to _ic are controlled to obtain good responsiveness. This is as follows. Figures a, b, and c show the magnetic flux φ of the three-phase induction motor 3 and the load current I _L (the load currents i _a , i _b , and i _c are collectively referred to as:
The same applies hereafter). Of these, Fig. 5b shows the magnetic flux φ when the value of the load current I _L is small, and Fig. 5c shows the magnetic flux φ when the value of the load current I _L is large.
(See FIG. 5a). That is, the phase difference φ ₀ with respect to the magnetic flux φ when the load current I _L is small is different from the phase difference φ _N with respect to the magnetic flux φ when the load current I _L is large, and there is a relationship such that φ _N >φo. Therefore, when the set speed of the induction motor 3 is changed, for example, when the load current I _L increases, the load current has the phase relationship shown in Fig. 5b.
Although I _L changes so as to maintain the phase relationship shown in FIG. 5c, there is a problem that the response characteristics in this case are poor. This is because the change in the load current I _L from the state shown in FIG. 5b to the state shown in FIG. 5c is gradual. Therefore, in the vector control, the load current I _L is forcibly changed from the state shown in FIG. 5b to the state shown in FIG. 5c. And this is the thyristor T ₁ to _{T 6} of current type three-phase inverter 1
This is done by ignoring the normal order and triggering as appropriate. However, an appropriate control method that combines the above two methods has not yet been proposed. This is the load current I _L
If there is a sudden change in current type three-phase inverter 1
This is because the control becomes extremely complicated as the conductive thyristor must be changed and the current vector must be controlled to the optimum position. More specifically, as shown in FIGS. 1b and 1c, the load current I _L is changed from the state shown in FIG. 5b to the state shown in FIG. Assuming that each shaded area is the commutation period T, Fig. 5b
For example, in the case of a load current i _a (see FIGS. 1 and 4) in the state shown in _FIG .
On the side its thyristor T ₁ or thyristor T ₃
Either one of them is conductive (see Figure 3). If the state shown in FIG. 5c is to be made here, at the above-mentioned change point C, the thyristor T ₃ is on the + side.
must be conductive, and either thyristor T ₂ or thyristor T ₄ must be conductive on the negative side (see FIG. 3). It is necessary to appropriately select the thyristors T ₁ to _{T 6} to be made conductive in this way and control the load current I _L so that the phase thereof is optimized. In view of the current situation, it is an object of the present invention to provide an economical and high-performance control method for a current-type three-phase inverter that combines the advantages of the PWM control method and the vector control method. The present invention, which achieves the above object, is based on the following principle as its technical idea. The explanation of the mode of changing the commutation period T based on the above-mentioned FIGS. 5a to 5c is an example, but the mode varies depending on the magnitude of change in the load current I _L and the time point C of change. Combinations are possible. Figures 6c to 6j list these combinations excluding the state of maximum change. That is, Fig. 6b is the waveform of the current load current I _L , and this is the waveform of Fig. 6c~
It changes to either one of Fig. 6j. For this explanation, as shown in FIG. 6a, the commutation period T (indicated by diagonal lines in the figure; the same applies hereinafter) after the positive side of the load current _I The load current I _L
The previous commutation period T on one side is in the state, followed by the steady state period on one side in the state, followed by -
Let the commutation period T after the positive side be in the state, the commutation period T before the + side following this be the state, and the subsequent steady state period on the positive side be the state, and which commutation period T and The steady state period is also 60°. Taking this as an example of the load current i _a and referring to Figure 3, the thyristor T ₁
- Table 1 can be obtained by making it correspond to the conduction of T ₆ .

【table】

[Table] On the other hand, when the current load current I _L changes to the states shown in FIGS. 6c and 6g, the states are maintained as they are. Similarly, if the changing states are divided into cases, the state when changing to the states shown in FIGS. 6 d and 6 e, the state when changing to the states shown in FIGS. 6 h and 6 i, and the state when changing to the states shown in FIGS. 6 h and 6 i,
When changing to the state shown in FIG. 6 f, the state changes to the state shown in FIG. 6, and when changing to the state shown in FIG. A quantitative analysis of this results in the following. As shown in Figures 6a to 6j,
θ = Phase difference from the start of the current state of load current I _L to the time of change C, α _T = Current load current
The phase difference from the beginning of the state of I _L to the end of the state of the load current I _L after the change is 0
<(α _T −θ)<60°, when the state is maintained; when −60°<(α _T −θ)<0, the state changes to: 60°<(α _T − When θ) < 120°, the state changes to . When -120° < (α _T − θ) < –60°, the state changes to 120 < (α _T − θ).
It is understood that when , the state changes to . In this way, it can be divided into five ways: when it changes to the state shown in Figure 6 f (when it changes to the state), and when it changes to the state shown in Figure 6 j (when it changes to the state) ) can be ignored for practical purposes. This is because when such a state occurs, the change in the load current I _L is very steep, and it can be assumed that such a steep change does not actually occur. Therefore, Table 2 is created by putting these together.

[Table] In this way, the operation according to the state change of the load current I _L is determined, but if we examine the more specific commutation process of the thyristors T ₁ to _{T 6} , we will find the following. The conduction thyristors T ₁ to _{T 6} in the changed load current I _L are connected to a predetermined PWM pattern and the change time point C in the changed load current I _L as shown in FIGS. 6 c to 6 j. From the beginning of the state to the point of change C
The phase difference α _N is determined from the phase difference α N . For example, if we consider the case where the load current i _a changes from the state shown in Figure 7a to the state shown in Figure 7b, in this case the state is maintained, so it is S mode, but conduction The thyristors T ₁ to _{T 6} to be pressed are the seventh
In the case of figure b, the thyristor T ₃ in the case of figure 7a,
Since the current changes from T ₂ to thyristors T ₁ and T ₂ , it is necessary to immediately perform commutation from thyristor T ₃ to thyristor T ₁ and set the time until the next commutation to δ. This is determined by calculating the interval α _N and making it correspond to the PWM pattern. Therefore, Table 3 summarizes the formula for calculating the time α _N for each mode.

[Table] In this way, each mode of M, S, and B is determined by calculating α _T -θ, and it is determined whether to advance one commutation period, within the same period, or return one commutation period. Furthermore, in a new PWM pattern at a point in time in response to a change in the load current I _L , the phase difference α _N from the start of the state to which the change point belongs to that change point, that is, the position of the change point within that state. The degree of existence α _N can be calculated.
Furthermore, within the state to which the change point belongs, the phase difference δ _N from the end of the state to the change point can be detected. The following method is used to perform commutation correction based on such calculations. That is, for example, as shown in FIG. 8, numbers are assigned to the positive, negative, and zero significant states of the PWM pattern. In this example, the numbers are from 0 to 8, but the numbers are from 0 to 2(m-1). Here, m is the number of PWM pulses. When this number is taken as the K number, the K number is obtained by calculating α _N using the new PWM pattern at the time of change. For example, time point C in FIG. 6g is like K=2 shown in FIG. Also, in the current PWM pattern shown in FIG. 6b, the change point can be obtained by the K number. In this way, commutation correction is performed using the K numbers, that is, K _s and K _N between the current PWM pattern and the new PWM pattern. During commutation correction, the PWM pattern is in two significant states, for example, K=1,
3, 5, and 7 are in the same significant state, K=2, 4,
6 and 8 are in other significant states. Furthermore, the currently conducting thyristors T ₁ T ₂ and T ₂ T ₃ in S mode,
The new conducting thyristors are also T ₁ T ₂ and T ₂ T ₃ . In M mode, the current conducting thyristor is T ₁ T ₂ T ₂ T ₃ ;
The new conducting thyristors are T ₂ T ₃ and T ₃ T ₄ . In B mode the currently conducting thyristors are T ₁ T ₂ and T ₂ T ₃ ;
The new conducting thyristors are T ₁ T ₂ and T ₆ T ₁ . Since the relationships between the two significant states and the currently conducting thyristor and the newly conducting thyristor match, the processing shown in FIGS. 9, S, M, and B becomes possible for each mode. Tables 4 and 5 show this relationship.
Table, Table 6.

【table】

【table】

[Table] FIG. 9 S and Table 4 show correction in S mode. First, K numbers are added to obtain Ks+K _N. Next, it is determined whether Ks+K _N is an even number or an odd number, and if it is an even number (Ks even number K _N even number or Ks odd number K _N odd number), the same conducting thyristors T ₁ and T ₂ are used, so there is no correction. In the case of an odd number (a combination of even and odd numbers for Ks and K _N ), K in the current PWM pattern
Determine whether the number Ks is even or odd. When Ks is an even number, the conducting thyristors are T ₁ and T ₂ , so the number corresponding to the new K _N becomes an odd number and the new conducting thyristor is
On the contrary, when K _S is an odd number, the conducting thyristors are T ₂ and _{T 3 ,} so the conducting thyristors corresponding to the new even number _{K N are} T ₁ and T ₂ . That is, when K _S is an even number, one forward rotation correction is performed, and when K _S is an odd number, one reverse rotation correction is performed. FIG. 9M and Table 5 show commutation correction in the M mode, and after obtaining K _S +K _N , it is determined whether K _S +K _N is an even number or an odd number. In the case of the M mode, the state changes from the + state on the left side to the one state on the right side as shown in FIG. When the judgment result of K _S + K _N is even or odd, the currently conducting thyristors T ₁ , T ₂ or T ₂ , T ₃ become new conducting thyristors T ₂ , T ₃ or T ₃ , T ₄ and once It will rotate forward. When it becomes an odd number, it is further determined whether K _S is an even number or an odd number, and when K _S is an even number, the conduction thyristor is changed to T ₁ ,
Since T ₂ becomes T ₃ and T ₄ , correction for normal rotation is performed twice, and when K _S is an odd number, the conduction thyristors T ₂ and T ₃ are not changed and there is no commutation correction. Further, FIG. 9B and Table 6 show B-mode commutation correction, where K _S +K _N is obtained and whether this value is even or odd is determined. In this B mode, the PWM pattern returns by one commutation period T. K _S + K _N
If is determined to be an even number, the current conducting thyristor T ₁ , T ₂ or T ₂ , T ₃ changes to the new conducting thyristor T ₆ , T ₁ or T ₁ , T ₂ according to the PWM pattern, so the reversal must be corrected once. become. If K _S +K _N is determined to be an odd number, then it is determined whether K _S is even or odd. K _S
If K is an even number, the conduction thyristors remain T ₁ and T ₂ , so no correction is necessary; if K _S is determined to be an odd number, the conduction thyristors are changed from T ₂ and T ₃ to T ₆ and T ₁ . Performs commutation correction of two reverse rotations. In Tables 4 to 6, current conduction thyristors refer to the thyristors T ₁ to T ₆ that are actually conducting at the time of change C, and new conduction thyristors refer to the state of the load current I _L at the time of change C after the change. _The thyristors _{T 1 to T 6 that} must be made conductive to create This refers to the case where the conduction thyristor changes in the order of T ₂ -> T ₄ -> T ₆ -> T ₂ , and "reversal" refers to the case where the above-mentioned order changes in the opposite direction. Therefore, depending on the magnitude relationship of α _T −θ, M, S, B
Select one of the modes, and then select each mode M,
The new conduction thyristor with respect to the current conduction thyristor in S and B is determined from the relationship with K _N based on the phase difference α _N , so the thyristor T ₁ to
By controlling the conduction of _T6 , it is possible to forcibly change the phase to the changed phase even during the commutation period T of the load current I _L. Embodiments of the present invention based on this knowledge will be described in detail with reference to the drawings. As shown in Fig. 10, in this embodiment, the load current I _L of the current type three-phase inverter (see Fig. 1) and the excitation current I which is obtained by converting the phase current of this load current I _L by three-phase/two-phase conversion. The secondary current calculation unit ₁₃ calculates I ₂ = √ _O ² _{+ L} ² based on
I ₂ and the excitation current Io are input to the phase difference detection section 14, and the phase difference φ between the two is calculated by calculating φ=tan ^-1 I ₂ /I ₀ , and sent to the α _T calculation section 15. The information is stored in the storage unit 16. That is, when the load current I _L supplied to the three-phase induction motor 3 (see Figure 1) changes due to load fluctuations, the phase difference α _T between the current load current I _L and the load current I _L after the change is calculated by the α _T calculation unit 16 via the magnetic flux φ. That is, α _T calculation unit 16
Now, input both the phase difference φo from the phase difference storage section 15, which stores the phase difference φo before the change in the load current I _L , and the phase difference φ _N after the change in the load current I _L from the phase difference detection section 14. Then, the calculation α _T =60°−(φ _N −φo) is performed (see FIGS. 5a to 5c). On the other hand, the phase difference θ
is stored in the θ storage unit 17, and its output is sent to the (α _T −θ) calculation unit 18. (α _T −θ)
The phase difference α _T calculated by the α _T calculation unit 16 is also sent to the calculation unit 18, where (α _T −θ)
By calculating the value of and sending it to the mode determining section 19, it is determined whether the mode is M, S, or B based on the magnitude relationship with respect to the commutation period T. Here, modes M, S, and B are specified. On the other hand, the α _N calculation section 20 calculates the phase difference α _N based on the output signal of the (α _T -θ) calculation section 18 and sends it to the PWM pattern storage section 21 . As a result, the phase difference α _N from the beginning of the state to which the change time point C of the load current I _L belongs after the change to the change time point C is stored. The PWM pattern storage section 21 stores a pattern for generating the load current I _L , which is converted into a time interval by the time exchange section 22 and becomes the clock pulse CLK of the ring counter 23 . This ring counter 23 uses its output signal to invert the thyristor of the current type three-phase inverter 1.
Trigger T ₁ to T ₆ as appropriate. At this time, the ring counter 23 has a forward/reverse rotation terminal ForR,
With the input to this, e.g. thyristor T ₁ →
A forward commutation of thyristor T ₃ and a reverse commutation of thyristor T ₃ →thyristor T ₁ are selected. The output of the PWM pattern storage section 21 is also input to the forward/reverse rotation terminal ForR, and by alternately selecting forward/reverse rotation during the commutation period T of the load current I _L , for example, the thyristors T ₁ , T ₃ are alternately conductive. The commutation correction storage unit 24 stores M, M, and M in FIG. 9 corresponding to the aforementioned modes M, S, and B.
The circuit functions of S and B are set, and commutation correction information shown in Tables 4 to 5 is stored. Functionally, the commutation correction storage section 24 stores the contents of the current conduction thyristor storage section 25 which stores the currently conduction thyristors T ₁ to _{T 6} based on the contents of the PWM pattern storage section 21 and the contents of the PWM pattern storage section 21 . It is clear from the above-mentioned K _S and K numbers that the contents are input. In this way, the commutation correction commands corresponding to modes M, S, and B determined by the mode determining section 19, that is, the number of commutations and either normal rotation or reverse rotation, are stored in the current conduction thyristor storage section 25 and the PWM pattern storage section 21. It is formed based on the contents and is sent out as a clock pulse CLK of the ring counter 23 and a forward/reverse selection pulse. As specifically explained above in conjunction with the embodiments, according to the present invention, even during the load current commutation period, the load current can be forcibly shifted to the changed load current.
This combines the features of the PWM control method, namely, the effect of low pulsating torque, and the feature of vector control, that is, the effect of good quick response.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a current type three-phase inverter together with its conventional control circuit and three-phase induction motor, Figure 2 is a waveform diagram of the load current that is its output, and Figure 3 is a diagram of the PWM control method. Explanatory diagram for explaining the conduction state of the thyristor, No. 4
The figure is a waveform diagram showing the waveform of the load current corresponding to this, Fig. 5a is a waveform diagram showing the magnetic flux, Figs. 5b and 5c are waveform diagrams showing the corresponding load current, Fig. 6 6a is a state diagram showing the state of the load current, FIG. 6b is a waveform diagram showing the current load current, FIGS. 6c to 6j are waveform diagrams showing the load current after change,
Figures 7a and 7b are waveform diagrams showing the current state and the state at the time of change in the load current.
The figure is an explanatory diagram showing an example of how to assign K numbers, Figure 9 M, S, and B are flowcharts showing three modes of commutation correction method, and Figure 10 is a block diagram showing an embodiment of the present invention. be. In the drawing, 1 is a current-type three-phase inverter, 3 is an induction motor, I _L is the load current, α _T , θ, α _N are the phase differences, and T
is the commutation period, C is the time of change, T ₁ , T ₂ , T ₃ , T ₄ ,
T ₅ and T ₆ are thyristors.

Claims (1)

[Scope of Claims] 1. A state that is a commutation period having a plurality of pulses of short duration in a predetermined period from the beginning of the positive load current for a three-phase induction motor,
This is followed by another state which is a steady period with one pulse of longer duration in a given period, followed by a commutation which has a plurality of pulses identical to said one state in a given period up to the positive end. In a method of controlling a current-type three-phase inverter that flows a PWM-controlled load current that has one more state, which is a period, and has six types of states with similar waveforms on the negative side, Calculate the secondary current I 2 from the load current I _L and the excitation current I ₀ obtained by converting this load current into 3-phase/ ₂ -phase, and calculate the phase difference φ between this secondary current I ₂ and the excitation current I ₀ . Calculate the phase difference α _T between the load current before and after the change from the memorized phase difference φ ₀ between the load current and exciting current I ₀ before the change and the phase difference φ _N after the change in the load current. Then, from the time when the steady period before the load current I _L changes to the commutation period, the change point C
The phase difference θ is calculated _from this phase difference θ and α _T , and the phase difference (α _T −θ), the load current I _L before the change, and the load current I _L change point C
The three modes SMB set for each period of the load current after the change to which the change point C belongs are selected by comparing the values based on the length of the period to which the change point C belongs, and the phase difference (α _T −θ) is calculated. From the start of the state to which the load current I _L changes after changing at the time C to the time C
The _PWM pattern for generating the load current I _L is calculated by calculating the phase difference α _N up to
0 to 0 to each positive, zero, and negative significant state of the PWM pattern
2(m-1) (m is the number of PWM pulses), and determine whether K _s + K _N is even or odd for each SNB mode based on the current K s and the changed K _N based on the phase difference α _N. In the case of a small number, the current conducting thyristor is commutated to the thyristor that should be conducting after the change by determining whether K _s is even or odd, and the clock pulse is generated using this correction command and the time-converted signal of the PWM pattern. By determining the forward or reverse rotation of the inverter's thyristor,
A method for controlling a current type three-phase inverter, characterized by outputting a thyristor control signal.