Control system for an inverter apparatus

• US 4,866,592 A
• Filed: 03/30/1988
• Issued: 09/12/1989
• Est. Priority Date: 03/30/1988
• Status: Expired due to Term

• Current Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Inventors: Nomura, Toshihiro, Fujii, Masaaki
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): Peckman, Kristine
• Application Number:
  US07/175,495
• Time in Patent Office: 531 Days
• Field of Search: 363/37, 363/56, 363/98, 363/126, 363/132
• US Class Current: 363/98
• CPC Class Codes: H02M 3/1555 for the generation of a regulated current to a load whose impedance is substantially inductive
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control system for a transistor inverter comprising a circuit for detecting the load current or the output voltage from the inverter to produce a detection output; a circuit for outputting a control instruction for adjusting the load current; a leading angle forming circuit for combining the detection output with the control instruction to form a control signal corresponding to a leading angle at which the inverter output voltage is controlled with a leading phase relative to the load current; and a circuit receiving the control signal from the leading angle forming circuit and for forming a switching control signal, which is supplied to the switching devices in the inverter. The load current is not controlled directly by controlling the frequency of the inverter, but by changing the phase difference γ between the load current and the inverter output voltage.

Claims

1. A control system for controlling an inverter supplying high frequency power to an inductive load in a series with a capacitor, said inductive load and capacitor forming a series resonant circuit having an alternating load current flowing therethrough, said invertor comprising semiconductor switching devices connected in the form of a bridge, each of said switching devices conducting current in a given direction and having a diode connected thereacross for conducting current in the direction opposite said given direction, a d.c. input voltage being applied to said inverter from a d.c. voltage source and an alternating output voltage leading said alternating load current by a predetermined phase angle being generated by said inverter and applied across said series resonant circuit, wherein the improvement comprises:

a zero-cross detector for detecting changes in the polarity of said alternating load current, said zero-cross detector generating a pulse each time said load current changes polarity;

a frequency detector for detecting the frequency of said alternating load current, said frequency detector generating a voltage proportional to said frequency;

a sawtooth wave generating circuit, having an integrator, coupled to the outputs of said frequency and zero-cross detectors, said sawtooth wave generating circuit integrating the voltage at the output of said frequency detector and being reset by the pulse at the output of said zero-cross detector to generate a sawtooth wave voltage synchronized with said alternating load current and having a constant amplitude;

a load current detector for detecting the magnitude of said alternating load current, said load current detector generating a d.c. voltage corresponding to the magnitude of said load current;

a current regulator coupled to said load current detector and adapted to receive an input signal corresponding to a desired value of said alternating load current, said current regulator comparing said input signal with the d.c. voltage generated by said load current detector and generating a current control voltage corresponding to said predetermined phase angle;

a comparator coupled to said sawtooth wave generating circuit and said current regulator for comparing said sawtooth wave and current control voltages, said comparator generating a pulse signal having a duration corresponding to said predetermined phase angle in accordance with said current control voltage; and

a switching control signal generating means coupled to said comparator and said semiconductor switching devices, said switching control signal generating means switching respective ones of said semiconductor switching devices in accordance with the pulse signal from said comparator, whereby said load current is controlled by changing said predetermined phase angle between said alternating load current and the alternating output voltage generated by said inverter.

2. The control system for controlling an inverter as claimed in claim 1 which further comprises delay means for delaying the control signal generated by said switching control signal generating means by a delay time corresponding to the turn-off time of said semiconductor switching devices.