JPH0697855B2 - How to protect the current source inverter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection method for a current source inverter, and more particularly to a protection method for preventing a short circuit in a direct current state and stably continuing the operation of the inverter. .

[Conventional technology]

The protection of the current source inverter is performed by preventing the positive side and negative side elements of the same phase from conducting at the same time and the short-circuit current flows (DC short-circuit state). Conventionally, the short circuit due to an erroneous pulse is prevented. Measures were being taken. In addition
In the AC motor control device described in 2599, the phase of the output current is changed by applying vector control, but since the operation that suddenly changes the output current phase angle command by 60 degrees or more is not assumed here, , Did not need any special protection measures.

[Problems to be solved by the invention]

In order to take advantage of the characteristic that the regenerative operation of the induction motor can be performed more easily than the voltage type inverter, it is desired to use a large capacity current type inverter. In this case, vector control with good control characteristics is used, but when controlling the torque generated by the motor over a range of several times the rated value, the phase difference between the exciting current and the output current, that is, the phase angle command of the output current Changes by ± 60 degrees or more. Then, there is a problem that a DC short circuit occurs due to the turn-off time of the elements forming the inverter, and the operation of the inverter cannot be continued.

An object of the present invention is to provide a method for protecting a current source inverter that can keep operating at a desired phase angle by preventing the inverter from being in a DC short-circuit state even if the output current phase angle command changes arbitrarily. To provide.

[Means for solving problems]

The above-mentioned purpose is to provide a mechanism for detecting the conduction state of each element at present and after commutation and setting the conduction state to the corresponding register, and comparing the contents of these registers to cause a DC short-circuit state. If it is predicted, before switching to the next conductive state, a gate signal for setting an intermediate state in which the elements of the positive arm and the negative arm of the phase in which a short circuit is predicted is brought into the non-conductive state at the same time is set to a predetermined value. This is achieved by outputting for a period.

[Action]

The intermediate state is provided for a period (ten-off time) for which the current that is currently flowing in the phase in which a DC short circuit is predicted is cut off. Therefore, after passing through this intermediate state, if the state is switched to the next state where a short circuit is expected, the short circuit state does not occur. This makes it possible to operate at a desired phase angle without causing a DC short-circuit state even if the output current phase angle command changes arbitrarily.

〔Example〕

Examples of the present invention will be described below. FIG. 2 shows a main circuit and a control unit of a current source inverter using the method of the present invention. AC power from an AC source 1 is rectified by a converter 2 driven by a gate circuit 7, and then a gate circuit. An inverter 4 driven by 8 converts the AC into a predetermined frequency and magnitude and supplies the AC to the electric motor 5.

The control unit 9 for controlling these is composed of a one-chip micro computer, and the speed command ω ₀ of the electric motor 5 which is a load.
And the feedback speed ω _r from the speed detector 16, the vector calculation processing unit 97 calculates the inverter frequency command ω ₁₀ , the output current phase angle command φ _0, and the DC current command i ₁₀ .
From the current command i ₁₀ and the DC current feedback signal i ₁ to the current control calculation unit 9
In 3, the phase command α ₀ of the converter 2 is calculated, and the direct current i ₁ is set to a desired value via the output pattern determination unit 91 and the gate circuit 7. On the other hand, the angle calculation unit 96, phi ₀
And ω ₁₀ calculate the angle command θ ₀ of the output current according to the equation (1).

θ ₀ = ∫ω ₁₀ dt + φ ₀ (1) The conduction state of each element of the pattern 4 corresponding to this θ ₀ is determined by the output pattern determination unit 94, and the short circuit prevention processing unit 92, which is a feature of the present invention, determines the short circuit prevention period. Gate circuit 8
Create a Yotsute gate signal U _P to _W-N to be applied to the gate of each element of the inverter 2.

Figure 3 is shows a waveform of a gate signal U _P to _W-N and the output current i _U through i _W of the inverter operation one period during steady-state operation, six one cycle 360 degrees modes 1 6 It is divided into modes. However, in this figure, the high level side represents the conductive state of the element, and the low level represents the non-conductive state. For example, in the mode 2, the elements of the V-phase negative arm and the W-phase negative arm are alternately turned on and off.

FIG. 4 shows a gate signal waveform when the angle command θ ₀ suddenly changes during such a steady operation and the mode is shifted from the mode 2 to the mode 5. The load condition of the motor 5 changes and each phase command φ ₁₀
It is fully conceivable that θ ₀ suddenly changes according to the equation (1) as a result of a large change in. And this θ ₀
When the sudden change timing corresponds to t ₁ to t ₃ , t ₁ to t ₄ , t ₂ to t ₃ , or t ₂ to t ₄ in FIG. 3, (a) in FIG.
To (d), respectively. Such an angle command θ ₀
In the case of a sudden change, the turn-off time of the main circuit element is much longer than the turn-off time.Because of the sudden change, the current of the element that changes from conducting to non-conducting before the turn-off time elapses The element that shifts from the non-conducting state to the conducting state is turned on. Therefore, in the case of FIG. 4 (a), the U phase and V phase, and in the cases of (b) and (c), the U phase,
In the case of (d), in the U phase and the W phase, a direct current short-circuit state occurs in which currents simultaneously flow in the positive electrode arm and the negative electrode arm.

In the present invention, in order to prevent such a short-circuit state and change the angle command θ ₀ to a desired value, FIG.
The short circuit prevention periods T _{A to} T _D are provided as shown in FIGS. 5 (a) to 5 (d) according to each state change of FIG. That is, in the case of FIG. 5 (a), the V-phase negative arm is commutated to the W-phase negative arm in the period T _A , and the U-phase positive arm is commutated to the V-phase positive arm in the period T _B , and finally the mode is set. Move to 5. In the case of FIG. 5 (b), the U-phase positive arm is commutated to the W-phase positive arm in the period T _C , and in the case of FIG. 5 (c), the U-phase positive arm to the V-phase positive arm in the period T _D. Divert to. In the case of FIG. 5 (d), the V-phase negative arm is commutated to the W-phase negative arm in the period T _E , and then the period is continued.
At T _F , the U-phase positive arm is commutated to the W-phase positive arm. At this time, the following conditions must be satisfied as the length of the short circuit prevention period.

T _A , T _C , T _D , T _E Turn-off time (2) T _A + T _B , T _E + T _F Allowable minimum pulse width (3) However, the allowable minimum pulse width is conduction delay time and commutation. It is the sum of the overlapping time. When the mode is shifted to the mode 5 in this way, the current of the phase in which a short circuit is predicted becomes zero in an intermediate state such as T _{A to} T _F , so that it is possible to cope with a sudden change in the angle command without causing a short circuit state. .

The case of FIG. 5 is an example of the angle command change from the mode 2 to the mode 5, but the similar DC short circuit phenomenon also occurs for the angle command change between other modes. FIGS. 6 and 7 show a method of providing a short circuit prevention processing period corresponding to all these mode changes. In these figures, the current conduction state OL
D, the state NEW to be conducted next, the conduction state (intermediate state) in the short circuit prevention period, and MID are shown. Arms with circles are in a conducting state, and the other arms are in a non-conducting state. FIG. 6 shows a case where a short circuit is predicted in one phase, and there are 12 patterns (a) to (l), and one short circuit prevention period is provided. Also, FIGS. 5 (b) and 5 (c).
Each case is shown in FIGS. 6 (a) and 6 (b).

FIG. 7 shows a case where a two-phase short circuit is predicted, and (a)-
There are 6 types of (f), and it is necessary to provide two short circuit prevention periods. This is because it is necessary to sequentially commutate the two phases in which a short circuit is predicted to the other phase. Here, in the case of FIG. 7, there are two ways of providing the short-circuit prevention period. However, what is common to these is that during the short circuit prevention period, the element of the positive electrode arm or the negative electrode arm of a phase in which a short circuit is not predicted must always be in the conductive state. The cases of FIGS. 5 (a) and 5 (d) are shown in FIGS. 6 (a) and 6 (f), respectively.

An example of the processing flow of the short-circuit prevention processing unit 92 (FIG. 2) for detecting cases where short circuits occur and providing a short-circuit prevention period for them, as shown in FIGS. 6 and 7. Is shown in FIG. 1 (a), and the configuration of the register group used therein is shown in FIG. 1 (b). Each register consists of 3 bits,
Registers OLDP and OLDN indicate the conduction states of the main circuit elements of the positive side and the negative side, respectively. Corresponding bit is 1
Conductive when the, shall apply in the non-conducting time of 0, the register OLDP of FIG. 1 (b), OLDN the elements of the current U _P phase and V _N-phase conduction,
Other examples show non-conduction. Also register NEWP, NEWN
Shows the next conductive state after the commutation. The above registers are set by the signal from the output pattern determining unit 94.

When these registers are set, first, Fig. 1 (a) is displayed.
At step 100, the short circuit is predicted by the following equation.

SHORT ← (OLDP * NEWN) + (OLDN * NEWP) (4) Here, the operations * and + take AND and OR for each bit of the two registers. Therefore, in the first AND operation on the right side, the phase in which the positive side was conducting before commutation (OL of the corresponding phase)
When the negative side of DP bit 1) becomes conductive after commutation (NEWN bit of the corresponding phase is 1), the bit of OLDP * NEWN corresponding to that phase becomes 1. That is, if the short-circuit prevention period is not provided, an output of 1 is obtained for a phase that short-circuits during commutation. The same applies to OLDN * NEWP, which is the second term on the right side of equation (4), and the corresponding bit becomes 1 if there is a phase whose conduction state can be switched from the negative side to the positive side before and after commutation. Therefore, in the value of the register SHORT obtained by the equation (4), 1 is set in the phase in which a short circuit is predicted, and in the example of FIG. 1 (B), two of the U and V phases correspond to it.

As a result of step 100, if all the bits of the register SHORT are 0 and there is no fear of short circuit, step 101 of FIG.
Outputs the values of registers NEWP and NEWN as gate signals to each element. If there is a short-circuited phase, step 102 checks whether it is one phase or two phases (corresponding to the number of 1 in SHORT). If there is one phase, step 103 determines the polarity of the short-circuited phase.
That is, if OLDP * SHORT = (0,0,0) (5), it is necessary to prevent a short circuit of the phase where the negative side is present and the positive side is conducting after commutation. It indicates that this is the case. Therefore, at this time, move to step 104,
Register MID1P indicating intermediate conduction status to prevent short circuit
(For positive side) Set the value of register OLDP which shows the current conduction state (the positive side of the relevant phase remains 0), and the value of register NEWN which shows the conduction state after commutation to the negative side register MID1N Is set (the negative side of the relevant phase is also 0). In this way, if the registers MID1P and MID1N are output as gate signals in step 106, 0 is output on both the positive and negative sides of the corresponding phase, and the corresponding element is turned off accordingly. Then step 10
If you move to 1, you can commutate without short circuit.

If equation (5) does not hold, it is positive as in step 104,
This is the case in FIGS. 6 (a) and 6 (b), etc. where the negative is the opposite, and accordingly the intermediate of the short circuit prevention is performed by the processing of step 105 in which P (positive) and N (negative) of step 104 are replaced. Register status M
Can be set to ID1P and MD1N.

If there is a two-phase short circuit as determined by step 102, then step 107a (or 107b) is first processed. Step 107a
In the process of, the register MID1P, MID1N is set as the first intermediate state of the two intermediate states required in the case of a two-phase short circuit, the positive side remains as it is (OLDP), and the negative side does not cause a short circuit. Set to the value (▲ ▼) that makes the switch conductive. As a second intermediate state, the register MID2P,
Each of the MID2Ns is set so that the positive side is in a state after commutation (NEWP) and the negative side is in the first intermediate state (▲ ▼). After this, in step 108, register MID1
If P, MID1N is output as the first intermediate state, then register MID2P, MID2N is output as the second intermediate state in step 109, and then commutation is performed in step 101, the commutation is completed without a short circuit. .

The processing of step 107a is the short-circuit prevention processing period shown in FIG.
When the left side of MID1 and 2 is selected, and when this is set to the right side of the figure, the processing of step 107b corresponds.

FIG. 8 shows an operation explanatory diagram in the additional embodiment of the present invention. In a commonly used semiconductor switching element, the turn-on time or turn-off time varies depending on the current value to be turned on and off, but it cannot be set to a desired time. However, a turn-off time and a semiconductor device that can change the turn-off time arbitrarily are conceivable. When a change in θ * such that a DC short-circuit state is predicted occurs, by controlling the turn-off time and turn-on time according to each arm, the processing as shown in FIG. It is possible to easily prevent a short circuit without performing the above. For example, FIG. 4 (a) of the above embodiment.
In the case of the state change as shown in FIG. 8, the gate signal is given as shown in FIG. At this time, turn off the U _P arm element and turn off the V _P arm element by T _A ,
The turn-on of the U _N arm element is delayed by (T _A + T _B ). This results in a change in the conduction state as shown in FIG. 8 (b), which is caused by the short circuit prevention period shown in FIG. 2 (a).
It becomes exactly the same as the case of.

In the above-described embodiment, the optimum short-circuit prevention period can be provided without being affected by variations in element characteristics, and reliable short-circuit prevention can be achieved.

〔The invention's effect〕

As is apparent from the above embodiments, according to the present invention, even if the load condition of the electric motor changes and the angle command of the output current suddenly changes, the DC short-circuit state of the inverter can be prevented.

[Brief description of drawings]

1 (a) and 1 (b) are flow charts showing an embodiment of the method of the present invention, FIG. 2 is a block diagram showing the configuration of the main circuit and control unit of the current source inverter, and FIG. The figure which shows the gate signal and output current waveform to the inverter of the figure, FIG. 4 is explanatory drawing of a DC short-circuit state, FIG. 5 is explanatory drawing of the application of the method of this invention with respect to each case of FIG. 4, FIG. FIG. 7 is a diagram showing a case where a one-phase short circuit and a two-phase short circuit occur and a method of preventing a short circuit at that time, and FIG. 8 is an explanatory waveform diagram of another embodiment of the present invention. 4 ... Current source inverter, 92 ... Short-circuit prevention processing section, 94 ...
... Output pattern determination unit, 96 ... Angle command calculation unit, _UP .
V _P, W _P ...... positive element gate signal, U _N. V _N , W _N ... Negative side element gate signal, T _A , T _B , T _C , T _D , T _E , T _F ... short-circuit prevention period, θ ₀ ... output current angle command, MID1P, MID1N, MID2P , MID
2 …… Register.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Mitsugu Matsutake, 3-1-1, Saiwaicho, Hitachi, Ibaraki Hitachi Ltd., Hitachi Works, Hitachi Plant (56) References

Claims (3)

[Claims] 1. When an output current phase angle of a vector-controlled current source inverter is switched by a sudden change of a current source inverter load, it is switched to an element having the same phase as that of a conducting element before switching but having a reverse polarity. An intermediate state in which two elements of the phase are detected as elements to be short-circuited when a conduction signal is given later and subsequently have an ignition pattern different from both the ignition patterns of the elements before and after the switching. A method for protecting a current source inverter, characterized in that the output current phase angle is switched via the. 2. When one short-circuited phase is detected as the short-circuited phase, in the intermediate state, both the positive-side element and the negative-side element of the short-circuited phase are non-conductive, and the short-circuited phase is present. In phases other than, the positive side element is equal to the conducting state of the positive side element before switching and the negative side element is equal to the conducting state of the negative side element after switching, or the positive side element is the positive side element after switching. The method for protecting a current source inverter according to claim 1, characterized in that the conduction state is equal and the negative side element is equal to the conduction state of the negative side element before switching. 3. When the number of short-circuited phases detected as the phases to be short-circuited is two, in the intermediate state, one of the positive side and negative side elements of the short-circuited phase is non-conductive. An intermediate state and a second intermediate state that follows the first intermediate state and in which the other positive side and negative side elements of the short-circuited phase are both non-conductive; The method for protecting a current source inverter according to claim 1, wherein, in the intermediate state, one of the positive side element and the negative side element of the phase other than the short-circuited phase is always in a conductive state.