Power converter for driving an AC motor at a variable speed
First Claim
1. A power converter for driving an AC motor at a variable speed, comprising:
- a thyristor converter connected to an AC power source for rectifying an AC voltage from said AC power source;
said thyristor converter having first and second DC terminals;
a DC intermediate circuit including a smoothing capacitor for charging therein a rectified output from said thyristor converter, a first diode, a second diode, a first semiconductor switch, a second semiconductor switch;
said smoothing capacitor having first and second terminals;
said first and second DC terminals of said thyristor converter being respectively connected to said first and second terminals of said smoothing capacitor through said first and second diodes, respectively, in a polarity relationship corresponding to forward conversion by said thyristor converter during driving of said AC motor; and
during braking operation of said AC motor, said first and said second DC terminals of said thyristor converter being respectively connected to said first and said second terminals of said smoothing capacitor through said first and second semiconductor switches, respectively, in a polarity relationship corresponding to reverse conversion by said thyristor converter, whereby during driving of said AC motor, one of said first and second semiconductor switches is turned off, while the other one of said first and second semiconductor switches is caused to perform a high frequency switching operation or both of said first and second semiconductor switches are simultaneously interrupted; and
during braking operation, one of said first and second semiconductor switches is rendered conductive while the other one of said first and second semiconductor switches is caused to perform a high frequency switching operation;
a voltage type inverter having two terminals respectively connected to two terminals of said smoothing capacitor for inverting a DC voltage across said two terminals of said smoothing capacitor into an AC voltage having a variable frequency and a variable voltage, said AC voltage being supplied to said AC motor;
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Accused Products
Abstract
A power converter having a thyristor converter connected to an AC power source to rectify its AC output, a DC intermediate circuit including a smoothing capacitor and receiving a rectified output from the thyristor rectifier and a voltage type inverter for converting a DC voltage applied from the DC intermediate circuit into an AC output voltage of a variable voltage and a variable frequency. The DC intermediate circuit has two series circuits, each having a diode and a transistor switch, connected in parallel with each other and to the both terminals of the thyristor converter. The junctions, each between the diode and the resistor, are connected to the both terminals of the smoothing capacitor. The two series circuits function to switch the connection polarities of the thyristor converter and the smoothing capacitor and to regulate the voltage across the capacitor with a limited current by a voltage step-up or step-down operation by the transistor switch.
60 Citations
11 Claims
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1. A power converter for driving an AC motor at a variable speed, comprising:
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a thyristor converter connected to an AC power source for rectifying an AC voltage from said AC power source;
said thyristor converter having first and second DC terminals;a DC intermediate circuit including a smoothing capacitor for charging therein a rectified output from said thyristor converter, a first diode, a second diode, a first semiconductor switch, a second semiconductor switch;
said smoothing capacitor having first and second terminals;
said first and second DC terminals of said thyristor converter being respectively connected to said first and second terminals of said smoothing capacitor through said first and second diodes, respectively, in a polarity relationship corresponding to forward conversion by said thyristor converter during driving of said AC motor; and
during braking operation of said AC motor, said first and said second DC terminals of said thyristor converter being respectively connected to said first and said second terminals of said smoothing capacitor through said first and second semiconductor switches, respectively, in a polarity relationship corresponding to reverse conversion by said thyristor converter, whereby during driving of said AC motor, one of said first and second semiconductor switches is turned off, while the other one of said first and second semiconductor switches is caused to perform a high frequency switching operation or both of said first and second semiconductor switches are simultaneously interrupted; and
during braking operation, one of said first and second semiconductor switches is rendered conductive while the other one of said first and second semiconductor switches is caused to perform a high frequency switching operation;
a voltage type inverter having two terminals respectively connected to two terminals of said smoothing capacitor for inverting a DC voltage across said two terminals of said smoothing capacitor into an AC voltage having a variable frequency and a variable voltage, said AC voltage being supplied to said AC motor; - View Dependent Claims (4, 5, 7, 8, 9, 10, 11)
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2. A control means for operating said thyristor converter substantially at a predetermined maximum forward conversion output voltage during driving of said AC motor, and for operating said thyristor converter substantially at a predetermined maximum reverse conversion output voltage during braking operation of said AC motor;
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- 3. an inductive element disposed in series with at least one of the AC and DC sides of said thyristor converter.
Specification