PWM inverter controller

Claim 2

In a PWM inverter (13) which, in an asynchronous operation mode of a low output frequency, performs an asynchronous operation in which the cut period remains constant irrespective of the change in the output fre­quency and which, in a synchronous operation mode of a high output frequency, performs a synchronous operation i which the cut period changes accompanying the change in the output frequency, an inverter controller which comprises: a frequency commander (20) for commanding a frequency that is to be produced by said inverter (13); a first signal generator (1) which receives the out­put F out of said frequency commander (20), and which, in said asynchronous operation mode of a small output, produces a signal (D(f)) of a magnitude that corresponds to said output and produces a signal of a predetermined magnitude in at least a low output frequency range in said synchronous operation region of a large output; a timing signal generator (4) which generates pulses of a predetermined period in said asynchronous operation mode, and generates pulse singals of a frequency that corresponds to the output of said frequency commander (20) in at least said low output frequency range in said synchronous operation mode; an adder (2) which adds up signals produced by said first signal generator (1) every time when a signal is produced from said timing signal generator (4), and produces a value obtained by subtracting an amount of 360 degrees from the added value when the phase of a sinus­oidal waveform generator (3) has exceeded 360 degrees; a phase detector (21) which detects the output of said adder (2) when it lies within a predetermined range; and a selector (22) which switches said asynchronous operation into said synchronous operation when the output of said frequency commander (20) exceeds a predetermined value and when it is detected from the output of said phase detector (21) that the output of said adder (2) lies within said predetermined range.

Claim 3

In a PWM inverter (13) according to claim 1, wherein said first signal is a digital signal and said first signal generator (1) is a digital singal generator (1).

Claim 4

In a PWM inverter according to claim 2, wherein a second digital signal generator (5) which, in response to the output of said first digital signal generator (1), produces a digital signal that increases with the increase of said output; said sinusoidal waveform generator (3) receives the output of said adder (2) to produce a sinusoidal waveform data of a phase corresponding to said output; a digital calculator (6) which receives the output of said second digital signal generator (5) and the out­put of said sinusoidal waveform generator (3) in synchro­nism with the timing signal produced by said timing sig­nal generator (4) to calculate a timing for generating a PWM signal; a PWM signal generator (7) for generating a PWM singal based upon the output of said digital calculator (6); and a drive circuit (9) is provided for forming a drive signal that will be supplied to the power element of said inverter (13) based upon the output of said PWM signal generator (7).

Claim 5

A PWM inverter controller according to claim 3, where­in said first digital signal generator (1) generates digital singals (D(f)) whose magnitude increases step­wisely with the increase in the output of said frequency commander (20) in said synchronous operation mode, and said timing signal generator (4) produces timing signals that change in the form of a saw tooth is a graph is described by plotting the output of said frequency commander (20) along the abscissa and by plotting the period of generating the timing signals along the ordinate.

Claim 6

In a PWM inverter (13) which, in an asynchronous operation mode of a low output frequency, performs an asynchronous operation in which the cut period remains constant irrespective of the change in the output frequency and which, in a synchronous operation mode of a high output frequency, performs a synchronous operation in which the cut period changes accompanying the change in the output frequency, an inverter controller which comprises: a frequency commander (20) for commanding a frequency that is to be produced by said inverter (13); a first signal generator (1) which receives the output of said frequency commander (20), and which, in said asynchronous operation mode of a small output, produces a signal of a magnitude that corresponds to said output and produces a signal of a predetermined magnitude in at least a low output frequency range in said synchro­nous operation region of a large output; a timing signal generator (4) which generates pulses of a predetermined period in said asynchronous operation mode, and generates pulse signals of a frequency that corresponds to the output of said frequency commander (20) in at least said low output frequency range in said synchronous operation mode; an adder (2) which adds up signals produced by said first signal generator (1) every time when a signal is produced from said timing signal generator (4), and produces a value obtained by subtracting an amount of 360 degrees from the added value when the phase of a sinus­oidal waveform generator (3) has exceeded 360 degrees; a phase detector (21) which detects the output of said adder (2) when it assumes a value that indicates the phase of just 360 degrees; and a selector (22) which switches said asynchronous operation into said synchronous operation when the output of said frequency commander (20) exceeds a predetermined value and when it is detected from the output of said phase detector (21) that the output of said adder (2) lies within said predetermined range.

Claim 7

In a PWM inverter (13) which, in an asynchronous operation mode of a low output frequency, performs an asynchronous operation in which the cut period remains constant irrespective of the change in the output frequency and which, in a synchronous operation mode of a high output frequency, performs a synchronous operation in which the cut period changes accompanying the change in the output frequency, an inverter controller which comprises: a frequency commander (20) for commanding a frequency that is to be produced by said inverter (13); a first signal generator (1) which receives the output of said frequency commander (20), and which, in said asynchronous operation mode of a small output, produces a signal of a magnitude that corresponds to said output and produces a signal of a predetermined magnitude in at least a low output frequency range in said synchro­nous operation region of a large output; a timing signal generator (4) which generates pulses of a predetermined period in said asynchronous operation mode, and generates pulse signals of a frequency that corresponds to the output of said frequency commander (20) in at least said low output frequency range in said synchronous operation mode; an adder (2) which adds up signals produced by said first signal generator (1) every time when a signal is produced from said timing signal generator (4), and produces a value obtained by subtracting an amount of 360 degrees from the added value when the phase of a sinus­oidal waveform generator (3) has exceeded 360 degrees; a phase detector (21) which detects the output of said adder (2) when it assumes a value that indicates the phase of just 360 degrees; and a selector (22) which switches said asynchronous operation into said synchronous operation when the output of said frequency commander (20) exceeds a predetermined value and when it is detected from the output of said phase detector (21) that the output of said adder (2) lies within said predetermined range.