JP2943323B2 - Method for detecting output current of PWM inverter - Google Patents

Description

The present invention relates to a control device for a PWM inverter, and more particularly to a method for detecting an output current of the inverter.

B. Summary of the Invention The present invention relates to a PWM inverter that generates each phase output from a voltage vector timing signal. By detecting the difference between the voltage vector and the center of the zero vector and correcting the current detection timing, deviation of the current detection timing due to inverter dead time and switching delay is eliminated.

C. Conventional technology PWM inverters enable high-performance speed control of AC motors such as vector control, and speed estimation using the primary voltage and current of the motor when vector control is performed without a speed sensor. It is necessary to detect the current of the motor for the comparison of the triangular wave in the tracking method.

In the current of the PWM inverter, the current ripple due to the switching frequency of the PWM and the fundamental wave current are superimposed. In order to detect the fundamental wave component from the current waveform, a method of removing harmonic components by a low-pass filter is known. I have.

In this method, the phase lag of the detection current becomes large, and the influence on the high-speed response becomes large in vector control and the like. PWM
As another method of detecting the current of the inverter at high speed, there is a method of sampling from a current waveform and setting this sampling timing as a vertex (break point) at which the PWM carrier signal (triangular wave) becomes maximum or minimum (for example, Hitachi Review ,
VOL65, NO.4 (1983-4), direct digital control of inverter by microprocessor). This method uses PWM
The switching operation point of the main switching element of the inverter is avoided, and the current is sampled almost at the intermediate point of the switching operation, thereby reducing the influence of the current ripple.

D. Problems to be Solved by the Invention The conventional current detection method in which the apex of a triangular wave is used as a current detection timing obtains a PWM waveform by comparing a triangular wave with a fundamental wave. In the time chart of FIG. The on-period period and the off-period period correspond to the center timings of the zero vector periods V ₀ and V ₇ of the output voltage vector (FIG. 5) when the induction motor stator takes complex coordinates. Become. Therefore, PWM waveform generation by triangular wave comparison method or PWM waveform generation from PWM pattern data
The inverter can remove the ripple current component by sampling the current at the center timing of the zero vectors V ₀ and V ₇ .

Here, the main circuit switch of the inverter has a small delay in the on / off control of both the high-side arm and the low-voltage side arm so as to prevent simultaneous ON (short circuit) when the ON and OFF are simultaneously switched. A time is provided.

Due to the delay time of the dead time, the delay of the dead time compensating circuit, and the switching delay of the switch element itself, a difference occurs between the zero vector time of the PWM waveform generating circuit and the zero vector time of the actual output voltage, and a ripple component occurs in the current detection. In some cases, when current detection is performed for speed estimation or the like, fluctuations in the detected current deteriorate speed detection accuracy.

An object of the present invention is to provide a current detection method that eliminates a shift in current detection timing due to dead time or switching delay.

E. Means and Action for Solving the Problems The present invention generates each phase output of the PWM inverter from a voltage vector timing signal in order to achieve the above object.
In the PWM inverter, the edge timing of the zero vector period is detected from the output voltage of the inverter, and the difference between this timing and the start / end timing of the zero vector period of the voltage vector timing signal is detected. The timing signal at the center of the zero vector of the timing signal is corrected, the output current of the inverter is sampled at the corrected timing to detect the current, and the zero vector of the zero vector timing signal for generating a PWM wave is detected. The difference between the start / end timing of the vector period and the start / end timing of the zero vector period of the output voltage vector of the inverter is detected as a dead time or switching delay, and the current at the top of the carrier wave is corrected by correcting the current sampling timing with this difference. Perform sampling.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The PWM calculation unit 2 of the microcomputer 1 calculates the start and end timing data T ₀ , T ₁ , T ₂ of each voltage vector period from the frequency and modulation degree command, and zero vector periods V ₀ , V ₇
The timing data T0 _-DET which is the center of is obtained. Gate signal generating unit 3 is timing data _{T 0-DET, T 0,} T 1, the gate having a width of T ₂ to end the output start of the voltage vectors V ₁ ~V ₆ output _{V U} ^*, V V ^*, V _W ^* is generated, and the phase sequence data at the time is obtained from the phase sequence table 4 which receives the phase of the modulation signal PWM_MOD as an input.

Gate output _{^{V U *, V V *,}} V W * is the gate signal of the inverter 5 drives the induction motor 6 from the inverter to obtain a voltage output of the PWM waveform. The PWM wave output voltage of each phase of the inverter 5 is detected as an on / off period by the voltage detection circuit 7 and is detected as a pulse having the width and timing of the zero vectors V ₀ and V ₇ by the logic circuit 8. Edge detecting circuit 9 ₁ to 9 ₄ respectively detecting the timing of the start and end of the zero vector. This timing is detected in the detection circuit 9 ₁ the end timing of the zero vector V ₀ is the on mode period in FIG. 4 for example, to detect the start timing of the zero vector V ₇ to the detection circuit 9 _2, the detection circuit 9 ₁ Output timing and detection circuit
9 ₂ of the output timing is the timing to sandwich the two periods of the vector V ₁ and V _6.

Delay time detector 10 ₁ to 10 _4, T _0, T ₂ the output voltage vector period of the PWM start and end timing T ₀ of the voltage vector V ₁ ~V ₆ of the computation unit _2, T _1, T 2 and the start and end of the reference timing is detected as a delay time difference ΔT between the detection timing of the edge detection circuit 9 ₁ to 9 _4. For example, from the falling timing T ₂ of the rise timing T ₀ and V ₁ of the fourth voltage vector of the combined voltage vector V ₆ and V ₁ was in off mode period diagram V _6, the actual relative detecting section 10 _1, T ₀ detects a difference [Delta] T _oN-S oN start timing, the detection unit 10 _2, T ₂
, The difference ΔT _ON-E of the _ON end timing with respect to.

The correction time calculators 11 ₁ and 11 ₂ calculate the correction times ΔT _OFF-DET and ΔT _ON-DET in the _ON mode and the OFF mode from the delay time ΔT detected by the delay time detectors 10 ₁ to 10 ₄ . These correction times are shown in the flowchart shown in FIG. 4 shows the generalized on-mode period and off-mode period of FIG. 4. Timings T ₀ , T ₁ , and T ₂ at which the output voltage vector command is obtained are calculated by the arithmetic unit 2 and the respective vector periods λ and μ are calculated. gate output V _U ^* to ^have, V _V ^*, the V _W ^* indicates that given to the inverter 5. Actual output voltage vector λ from the inverter 5 at this time ', mu' is detected as an edge timing edge detecting circuit 9 ₁ to 9 _4,
Delay time [Delta] T of the delay time detector 10 ₁ to 10 ₄ delay time [Delta] T _ON-S in the on mode, [Delta] T _ON-E and off mode
_OFF-S and ΔT _OFF-E are detected respectively. From these delay times, the correction times of the correction time calculation units 11 ₁ and 11 ₂ are calculated based on the actual voltage vector outputs λ ′ and μ ′ with respect to the voltage vector commands λ and μ.
Of start delay and end delay Asking.

Next, the timing correction unit 12 corrects the correction time ΔT _OFF-DET , ΔT
_ON-DET is _added to or subtracted from zero vector timing TO _-DET . In this correction, as shown in FIG. 2, the correction time ΔT _ON-DET detected in the previous ON mode period is used as the correction amount of the next zero vector timing, and similarly, the correction time detected in the previous ON mode period is used. The time ΔT _OFF-DET is used as the correction amount of the next zero vector timing. By these corrections, the zero vector timing is corrected to the center of the zero vector of the actual output voltage vector, that is, to the zero vector timing corrected by the dead time and switching delay on the inverter 5 side.

Therefore, the current detection of the motor 6 is performed by a sample-and-hold circuit.
Eliminating the occurrence of current ripple due to a shift due to dead time, etc. by sampling at zero vector timing corrected by the timing correction unit 12 when sampling with 13 _{1 to} 13 ₃ and A / D converters 14 _{1 to} 14 ₃ Can be.

Each operation of the microcomputer 1 described above is realized by a flowchart shown in FIG. In the figure, the steps
S1 to S8 are the differences ΔT _ON-S , ΔT _ON-E , ΔT _OFF-S , ΔT _OFF-E from the timings T _{1 to} T ₃ and the start and end timings of the zero vector.
In step S9, the timing T _O-DET and T _{0 to} T ₂ are calculated.In step S11, the corrected timing T _O-DET in the on mode is obtained, and in step S12, the corrected timing T _O in the off mode. _-DET is obtained, and in each case, the timing obtained in step S9 is set in T _ON-S or the like. In step S13, each timing data is set as a gate control command signal and also as a current sampling signal.

G. Effects of the Invention As described above, according to the present invention, the difference between the start and end timings of the respective zero vector periods of the voltage vector timing signal for generating the PWM waveform and the output voltage vector is detected. The center timing of the zero vector is corrected so that the sampling of the current can be performed without the dead time set in the main switch of the inverter or the shift of the center of the zero vector due to the switching delay. High-precision speed control is enabled from detection and, consequently, speed estimation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a time chart of a correction time calculation in the embodiment, FIG. 3 is a flowchart of another embodiment, and FIG. 4 is a triangular wave comparison method in a PWM inverter. FIG. 5 is a voltage vector diagram. 2 ... PWM operation unit, 3 ... Gate signal generation unit, 4 ... Phase sequence table, 9 ₁ , 9 ₄ ... Edge detection circuit, 10 ₁ , 10 ₄ ...
Delay time detector, 11 ₁ , 11 ₂ … Correction time calculator, 12…
Timing correction unit.

Continuation of the front page (56) References JP-A-63-80774 (JP, A) JP-A-2-189467 (JP, A) JP-A-2-262873 (JP, A) JP-A-2-307070 (JP) , A) JP-A-3-65058 (JP, A) Kodama and three others, "PWM synchronous current detection method", Proceedings of the National Convention of the Institute of Electrical Engineers of Japan in 1991, 5-118 (58) Field surveyed (Int. Cl. ⁶ , DB name) H02M 7/42-7/98 JICST (JOIS)

Claims (1)

(57) [Claims] 1. A PWM inverter for generating each phase output of a PWM inverter from a voltage vector timing signal.
The edge timing of the zero vector period is detected from the output voltage of the inverter, and the difference between this timing and the start / end timing of the zero vector period of the voltage vector timing signal is detected. A current detection method for a PWM inverter, comprising: correcting a timing signal at the center of the zero vector of (1), sampling the output current of the inverter at the corrected timing, and detecting the current.