JP3393036B2 - Control device for PWM converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a control device for a converter that converts AC to DC by pulse width control, and more particularly to a device for stably generating an AC reference sine wave. Things. 2. Description of the Related Art Generally, in AC control of a converter, it is often necessary to generate a reference sine wave synchronized with a power supply voltage in order to generate a sine wave command value. Therefore, it is necessary to provide a control device that detects the zero-cross point of the power supply voltage and adjusts the frequency and phase of the reference sine wave so as to match the frequency and phase of the power supply. In order to adjust the phase of a reference sine wave, two types of methods have conventionally been used. The first method is to simply reset the phase of the reference sine wave at the power supply phase at the detection point each time the power supply crosses zero, and then add (integrate) the estimated power supply frequency to set the phase. It is a method to ask. The principle of another method is illustrated in the block diagram of FIG. In FIG. 2, reference numeral 7 denotes a phase controller, which amplifies the deviation between the power supply voltage phase value (θcross) at the time of power supply voltage zero crossing and the phase value (θc) of the reference sine wave at that time, and amplifies the frequency. Δωc) is output. Reference numeral 6 denotes a frequency control loop, which amplifies the deviation between the command value and the reference sine wave frequency so that the reference sine wave frequency (ωc) matches the given command value, and updates the reference sine wave frequency. Adjust. The command value is the sum of the output (Δωc) of the phase controller 7 and the detection value (ωs) of the power supply frequency (zero cross frequency). Reference numeral 41 denotes an integrator for adding the frequency of the reference sine wave output from the frequency control loop 6 to determine the phase (θc). [0005] However, there are the following problems. The first method is simple, but when the power supply frequency is not accurately known or fluctuates, the reference sine wave frequency deviates from the power supply frequency, and the phase error accumulates immediately before the next zero crossing, and the zero point at the zero crossing point When reset, the reference sine wave becomes discontinuous and cuts, adversely affecting the AC control loop. On the other hand, in the second method, the waveform of the reference sine wave is continuous without resetting the phase, but the configuration is a double loop of frequency and phase, which is complicated. In addition, in order to leave no offset in the phase error, an integrator must be provided in the phase controller, the frequency amplifier, or both. When the integrator 41 is included, the order of the loop becomes 2 or more. Therefore, it is difficult to secure the stability margin of the loop, and the loop is easily broken when the power supply fluctuates. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to solve these drawbacks, to have a simple configuration, and to provide a PW capable of stably generating a reference sine wave.
An object of the present invention is to provide a control device for an M converter. [0007] That is, a means for achieving the object is a PWM for converting an AC power supply to a DC.
A converter converter, a zero-cross period detector of the power supply voltage, a reference sine-wave generator that generates a sine-wave AC command based on the zero-cross detection time, and a conversion so that an AC control amount matches the AC command value. A reference sine wave generator of a PWM control converter comprising: an AC controller that outputs an open / close signal of a semiconductor switch element that constitutes a switch.
A first means for obtaining a power supply voltage zero-cross frequency detection value through a low-pass filter to obtain a power supply average frequency (ωs bar); And a second means for calculating the reference sine wave frequency (ωc) by adding the average power supply frequency obtained by the first means and the reference sine wave incremental frequency obtained by the second means. The third means is provided, and a reference sine wave is generated based on the output of the third means. An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the frequency of the power supply is estimated by the first means 1 and the phase of the reference sine wave is changed by the second means 2 to the phase of the power supply voltage. If it deviates, an incremental frequency for accelerating or decelerating the phase is generated. Then, the third means 3 adds the outputs of the first means 1 and the second means 2 to determine the frequency ωc of the reference sine wave. The phase of the reference sine wave can be obtained by the integrator 4 at the reference sine wave frequency obtained by the third means 3. In such a configuration, when the power supply voltage angular frequency is represented by ωs, the phase θs is represented by the following equation (1). [0009] Here, t is a time variable, and is defined as a starting point 0 when the power supply voltage crosses zero. The power supply frequency can be obtained by measuring the period of the zero crossing between the previous time and the current time with a timer, but the value may be changed every time due to voltage fluctuation, switching ripple, noise, or the like. If the frequency measured every time is directly used for calculating the reference sine wave phase, it is difficult to obtain a gentle reference sine wave for the above-described reason. The first means 1 of the present invention is a means for obtaining an average frequency ωs by low-passing a measured frequency value. The average frequency obtained by this means is considered to be an ideal power supply frequency from which influences such as switching ripple and voltage fluctuation are removed. Can be If this is used for phase calculation, a stable reference sine wave can be obtained. Also, when the power supply frequency changes, it is clear that the average frequency can follow the power supply frequency without offset with a slight delay due to the average calculation. Various types of low-pass filters may be applied, but the temporary delay filter shown in equation (2) is the simplest. ## EQU2 ## Here, s represents a Laplace operator, and τ is a time constant of a low-pass filter. Reference sine wave phase θ
c can be calculated as in equation (2) in the same manner as in equation (1). [0013] However, in this method, it is necessary to reset θc to θcross every time the zero-crossing detection point occurs.
θcross is a value calculated from the detection circuit constant on the assumption that the power supply is in a steady state, and when there is the above-described power supply fluctuation, switching ripple, or the like, a problem similar to the frequency occurs. When there is a difference between the average frequency and the power supply frequency ωs,
The phase of the reference sine wave gradually departs from the phase of the power supply.
When resetting occurs, the waveform becomes discontinuous as described in the related art. In order to continuously generate the phase of the reference sine wave, accumulation is performed based on the previous values without resetting even at the zero-cross point. In order to prevent the phase shift, the second
In the means 2, the power supply phase θcross at the zero-cross point is
And the difference between the phase of the reference sine wave and the phase of the reference sine wave at that time are amplified, and an increment Δωc of the reference sine wave frequency is calculated. Then, the third means 3 calculates the frequency of the reference sine wave by adding the frequency increment to the average value of the power supply frequency, accelerates / decelerates the speed at which the phase advances, and gradually converges the phase difference to zero. So that In FIG. 1, the amplifier of the second means 2 can be generally constituted by a PI controller. However, since the output of the first means 1 matches the steady value of the power supply frequency,
Even if there is no integral controller, that is, even if it is simply constituted by a proportional unit, a phase error offset does not theoretically remain. Since the use of an integrator is unnecessary, the order of the loop is 1 for each of the 4 integrators. Therefore, stability is always ensured. As described above, the first means 1 of the present invention can estimate the frequency of the power supply without an offset, and can generate a stable reference sine wave. When there is a phase synchronization initial error, the second means 2 accelerates / decelerates the reference sine wave frequency so as to eliminate the error. The third means 3 constitutes a reference sine wave generating apparatus which is stable and has no error offset by adding the outputs of the first and second means to obtain the frequency of the reference sine wave. As described above, according to the present invention, a reference sine wave having a simple configuration and high waveform stability can be generated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of a principle of generating a reference sine wave according to the present invention. FIG. 2 is a block diagram illustrating a conventional principle of generating a reference sine wave. [Description of Signs] 1 First Means 2 Second Means 3 Third Means 4, 41 Integrator 5, 51 Sampling & Holder 6 When Power Supply Voltage Is Zero Crossed 6 Prior Art Frequency Controller 7 Prior Art Phase Controller T Time variable τ Time constant of low-pass filter ωs Power supply frequency detection value ωs bar Power supply frequency average value Δωc Reference sine wave frequency increment ωc Reference sine wave frequency θc Reference sine wave phase θcross Power supply zero cross phase

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/21 G05F 1/00 H03L 7/08

Claims (1)

(57) [Claim 1] A PWM converter converter for converting an AC power supply to a DC power, a zero-cross period detector of the power supply voltage, and a sine-wave AC command based on the zero-cross detection time. A reference sine wave of a PWM control converter, comprising: a reference sine wave generator for performing a switching operation; and an AC controller for outputting an opening / closing signal of a semiconductor switch element constituting a converter so that an AC control amount matches the AC command value. First means for obtaining a power supply voltage zero-cross frequency detection value through a low-pass filter to obtain a power supply average frequency (ωs bar) in the generator; A second means for obtaining the frequency (Δωc), and adding the average power supply frequency obtained by the first means and the reference sine wave increment frequency obtained by the second means. And provided third means for obtaining a reference sine wave of a frequency (.omega.c), the third PWM converter and generates a reference sine wave based on the output of the means of the control device.