JPH03103078A - Pulse width modulation pulse generator - Google Patents

Abstract

PURPOSE:To suppress a beat of a voltage and to improve controllability by synchronizing the frequency of a carrier with an integral multiple of 3 of a modulation wave in a high modulation frequency range to generate a PWM pulse, maintaining a carrier frequency constant in a low frequency range, and generating an asynchronous PWM pulse. CONSTITUTION:A timing pulse generator 21 inputs timing pulses for detecting time points of 90 and 270 degrees of phase of a carrier to an asynchronous pulse generator 24. A triangular-shaped carrier and a modulation wave cross once from 90 to 270 degrees of the phase of the carrier and cross once from 270 to next 90 degrees. Then, first time T1 to crossing with the timing pulses of the 90 and 270 degrees as references is calculated by a first time calculator 22, and second time T2 is calculated by a second time calculator 23. Data are applied to the generator 24 to form an asynchronous PWM pulse.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention generates pulse width modulation pulses with a carrier wave synchronized with the modulated wave when the frequency of the modulated wave is high;
Relating to a pulse width modulation pulse generator that generates pulse width modulation pulses with a carrier wave being asynchronous when the frequency of a modulated wave is low, and that can smoothly switch from synchronous to asynchronous or from asynchronous to synchronous. .

[Conventional technology]

A sinusoidal modulated wave and a frequency higher than this modulated wave
By comparing the magnitude relationship with the square waveform carrier wave, a pulse width modulated pulse train is obtained, so this pulse width modulated (hereinafter abbreviated as PWM) pulse is used in an inverter that converts direct current to alternating current. This makes it possible to efficiently convert a sinusoidal waveform to alternating current with a low harmonic content, and such an inverter is called a PWM inverter. By the way, with this PWM inverter, when the frequency of the modulated wave is changed, the frequency of the output AC changes accordingly, so it is possible to use a PWM inverter as a power source for an induction motor, which conventionally had difficulty controlling its speed. Since it can be driven at a desired speed, it has become widely used.

[Problem to be solved by the invention]

Conventionally, when generating the above-mentioned PWM pulse, pulse width modulation was performed with the modulated wave and carrier wave being asynchronous. When driving a large-capacity motor with a PWM inverter, the semiconductor switching elements that make up the inverter have a risk of not being able to increase the switching frequency. This has the disadvantage that the output voltage of the PWM inverter fluctuates.

Therefore, the purpose of this invention is to avoid the inconvenience of voltage beats by synchronizing the modulated wave and the carrier wave. However, if the carrier wave is synchronized even when the modulated wave has a low frequency, there is a problem that the frequency of this carrier wave will become low, so this problem is also attempted to be solved. (Means for Solving the Problems) In order to achieve the above object, the pulse width modulation pulse generator of the present invention establishes a magnitude relationship between a variable frequency modulation wave and a triangular waveform modulation wave. By comparing, in a device that generates pulse width modulation pulses, there is a pulse generating means that generates a pulse train with a frequency proportional to the frequency command value of the modulated wave, and a pulse train that counts up when rotating in the forward direction and down when rotating in the reverse direction. An up/down counter for counting, a memory that stores the data of the carrier wave and inputs the signal from this amplifier down counter, and a signal from this memory and a separately set modulation rate signal are input, and both are input. a digital comparator that outputs a pulse for synchronous pulse width modulation by comparing the magnitude relationship; and a timing pulse generating means that generates a pulse at a first time point when the phase of the carrier wave is 90 degrees and a second time point when the phase is 270 degrees; a first time calculation means for calculating a first time from the first time point until the carrier wave and the modulated wave intersect between the 90 degree phase and the 270 degree phase of the carrier wave; and from the second time point,
a second time calculation means for calculating a second time until the carrier wave and the modulated wave intersect between the 270 degree phase of the carrier wave and the 90 degree phase of the next cycle; An asynchronous pulse generating means that inputs a second point in time and a second time and generates an asynchronous pulse width modulation pulse, and switches between the synchronous pulse width modulation pulse and the asynchronous pulse width modulation pulse from synchronous to To asynchronous, a switching command is issued when the phase of the modulated wave is 0 degrees, 120 degrees, or 240 degrees, and from asynchronous to synchronous during forward rotation, the phase of the modulated waves is 0 degrees, 120 degrees, or 240 degrees. A switching command is issued when the phase of the carrier wave is between 270 degrees and 360 degrees, and the phase of the modulated wave is 0 degrees, 120 degrees, or 240 degrees when changing from asynchronous to synchronous during reverse rotation. synchronous/asynchronous switching means that issues a switching command when the phase of the carrier wave is between 0 degrees and 90 degrees; 14. It is assumed that there is a data selector that selects the Halsnoys for use.

[Effect]

In the region where the frequency of the modulated wave is high, the present invention sets the frequency of the carrier wave to an integral multiple of 3 of the frequency of the modulated wave, and generates a PWM pulse in a state where both are synchronized.
The aim is to suppress voltage beats, reduce switching loss, and reduce harmonics. Furthermore, in a region where the modulated wave frequency is low, the carrier wave frequency is kept constant to generate asynchronous PWM pulses, thereby improving controllability. For this purpose, it is necessary to switch between the Mp WM pulse and the asynchronous PWM pulse, but as mentioned above, the synchronous PWM pulse
Since the modulation ratio at the time of WM pulse generation is an integral multiple of 3, when the phase of the modulated wave is 0 degrees, 120 degrees, or 240 degrees, the phase of the carrier wave is 0 degrees, and the slope is the same. By selecting this point in time to switch between synchronous PWM pulses and asynchronous PWM pulses, it is possible to avoid forced synchronization of carrier waves and to achieve smooth switching.

〔Example〕

Figure 1 is a diagram showing an embodiment of the present invention. In FIG. 1, a frequency signal of a modulated wave sent as n1-bit data is replaced by a series of pulse trains in a pulse generating circuit 11. In FIG.

FIG. 2 is a circuit diagram showing the configuration of the pulse generation circuit shown in the embodiment circuit of FIG. , 17B-...17C. With this arrangement, a pulse train of D1 to D1 with a frequency proportional to the frequency data of nl bits is output from this pulse generation circuit.
In the circuit shown in the figure, the frequency of the pulse train changes continuously in response to changes in data D, to D71. The up/down counter 12 is triggered by the pulse outputted by the pulse generation circuit 11 shown in FIG.
For example, if the rotation direction command is for forward rotation, it is counted up, and when it is reversed, it is counted down.
Form address data of memory l3 of n2 bits. This memory 13 stores triangular wave data of a triangular waveform carrier wave, so when the output of this memory 13 and the modulation rate signal are input to the digital comparator 14, the synchronized PWM pulse is generated by comparing the two. is created and sent to the data selector 12. Furthermore, this PWM
When using pulses for a 3-phase inverter, memory 1
3 naturally outputs three-phase data whose phases are shifted by 120 degrees from each other.

Even in a region where the modulated wave frequency is low, if the carrier wave frequency is made proportional to the modulated wave frequency, this carrier wave frequency value becomes small, causing problems such as a decrease in controllability. Therefore, even if the modulated wave frequency falls below a predetermined value, the carrier wave frequency is maintained at a constant value to avoid the above-mentioned disadvantage, but at this time the carrier wave becomes asynchronous with the modulated wave.

FIG. 3 is an operation waveform diagram showing the operation of the asynchronous pulse generation circuit shown in the embodiment circuit of FIG.
A) is the waveform of the modulated wave and carrier wave, and Figure 3 (opening) is the asynchronous P
Figure 3 (c) shows the changes in the WM pulse and the timing pulse. The timing pulse generation circuit 21 in FIG. 1 inputs timing pulses (see FIG. 3 (c)) that detect the time point when the phase of the carrier wave is 90 degrees and 270 degrees to the asynchronous pulse generation circuit 24. .

The triangular waveform carrier wave and modulated wave intersect once between 90 degrees and 270 degrees, and the phase of the carrier wave is 270 degrees.
It intersects once between degrees and 90 degrees of the next cycle (
(See Figure 3 (a)). Therefore, the first time calculation circuit 22 calculates the first time T1 until the carrier wave and the modulated wave intersect, based on the timing pulses at 90 degrees and 270 degrees.
The second time T2 is calculated by the second time calculation circuit 23, and the respective data are sent to the asynchronous pulse generation circuit 24.
The asynchronous PWM pulse shown in FIG. The synchronous/asynchronous switching circuit 25 instructs the data selector 26 to switch at an appropriate timing in response to the issuance of a synchronous/asynchronous switching command (that is, when the frequency of the modulated wave passes the above-mentioned predetermined value). However,
This switching is performed when the following conditions are satisfied. a) Non-synchronous 71, I PWM pulse from synchronous PWM pulse
Switching to Hals is performed when the voltage phase of the modulated wave is 0 degrees, 120 degrees, or 240 degrees, regardless of whether the rotation is forward or reverse.

b) Switching from non-synchronized g p WM pulses to identical MP WM pulses is performed when the voltage phase of the modulated wave is 0 degree or 1 degree during forward rotation.
This is done at either 20 degrees or 240 degrees and the carrier phase is between 270 degrees and 360 degrees.

c) Switching from non-uniform XIPWM pulses to homogeneous O p WM pulses is performed when the voltage phase of the modulated wave is zero or 12 degrees during reverse rotation.
0 degrees or 240 degrees, and the carrier phase is between 0 degrees and 9 degrees.
This is done at a point between 0 degrees.

As mentioned above, since the modulation ratio is an integer multiple of 3,
Since the carrier wave phase is 0 degrees when the modulated wave phase is 0 degrees, 120 degrees, and 240 degrees, switching between synchronous and asynchronous modes can be performed smoothly. [Effects of the Invention] According to the present invention, when the modulating wave frequency is equal to or higher than a predetermined value, the carrier wave frequency is set to an integral multiple of 3, and the PWM pulse is generated while both are synchronized. When the modulated wave frequency is below the predetermined value, by setting the carrier wave frequency to a constant value, P
By controlling the WM pulse, it is possible to reduce harmonics and switching loss in the high frequency region, and to improve controllability in the low frequency region. Furthermore, smooth switching between synchronous and asynchronous modes can be achieved by switching between synchronous and asynchronous modes at appropriate timing when the carrier wave is at zero phase. Therefore, if this PWM pulse generator is applied to an inverter to drive an electric motor, the electric motor can smoothly operate in a wide speed range from low speed to high speed.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an embodiment of the present invention, Figure 2 is a block diagram showing an embodiment of the present invention.
The figure is a circuit diagram showing the structure of the pulse generation circuit shown in the embodiment circuit of Fig. 1, and Fig. 3 is an operation waveform diagram showing the operation of the asynchronous pulse generation circuit shown in the embodiment circuit of Fig. 1. It is. 11...Pulse generation circuit, 12...Up/down counter, 13...Memory, l4...Digital comparator, 15...Chronok, 16A, 1
6B, 16C...adder, 17A, 17B, 17C...
...Flimb flop, 21. ．． ．． Timing pulse generation circuit, 22...first time calculation circuit, 23...second
Time calculation circuit, 24...Asynchronous pulse generation circuit, 25
...Synchronous/asynchronous switching circuit, 26...Data selector. ),・No Man 1 Figure

Claims (1)

[Claims] 1) By comparing the magnitude relationship between a variable frequency modulated wave and a triangular waveform modulated wave, a device that generates pulse width modulation pulses can generate a pulse train with a frequency proportional to the frequency command value of the modulated wave. a pulse generating means for generating a pulse train; an up-down counter that counts up the pulse train during forward rotation and down-counts during reverse rotation; a memory that stores data of the carrier wave and inputs signals from the up-down counter; signals from memory and
A digital comparator that inputs a separately set modulation rate signal and outputs a pulse for synchronous pulse width modulation by comparing the magnitude relationship between the two, a first point in time when the phase of the carrier wave is 90 degrees, and a phase at 270 degrees. a timing pulse generating means that emits a pulse at a second point in time, and calculates a first time from this first point in time until the carrier wave and the modulated wave intersect between the 90 degree phase and the 270 degree phase of the carrier wave. a first time calculation means; a second time for calculating a second time from the second point in time until the carrier wave and the modulated wave intersect between the 270 degree phase of the carrier wave and the 90 degree phase of the next cycle; a calculation means; an asynchronous pulse generation means for generating an asynchronous pulse width modulation pulse by inputting the first time and the first time and the second time and the second time; and the synchronous pulse width modulation pulse. Switching from synchronous to asynchronous with the asynchronous pulse width modulation pulse is performed when the phase of the modulated wave is 0 degrees or 12 degrees.
A switching command is issued at 0 degrees or 240 degrees, and from asynchronous to synchronous during forward rotation, the phase of the modulated wave is 0 degrees or 12 degrees.
0 degrees or 240 degrees and the phase of the carrier wave is 27
A switching command is issued at a certain point between 0 degrees and 360 degrees, and from asynchronous to synchronous during reverse rotation, the phase of the modulated wave is 0 degrees, 120 degrees, or 240 degrees, and the phase of the carrier wave is from 0 degrees. A synchronous/asynchronous switching means that issues a switching command at a certain point in the range up to 90 degrees, and selecting either the synchronous pulse width modulation pulse or the asynchronous pulse width modulation pulse according to the command of the synchronous/asynchronous switching means. 1. A pulse generator for pulse width modulation, comprising: a data selector for pulse width modulation;