Modular power supply with PLL control

• US 4,783,728 A
• Filed: 07/08/1987
• Issued: 11/08/1988
• Est. Priority Date: 04/29/1986
• Status: Expired due to Fees

• Current Assignee: Modular Power Corp.
• Original Assignee: Modular Power Corp.
• Inventors: Hoffman, David C.
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): Sterrett, Jeffery
• Application Number:
  US07/071,586
• Time in Patent Office: 489 Days
• Field of Search: 307/82, 363/34, 363/37, 363/65, 363/71
• US Class Current: 363/37
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel
• CPC Class Codes: H03K 17/04126 in bipolar transistor switches
• CPC Class Codes: H03K 17/0422 Anti-saturation measures
• CPC Class Codes: H03K 17/567 Circuits characterised by the use of more than one type of semiconductor device, e.g. BIMOS, composite devices such as IGBT

Abstract

An uninterruptible power supply includes removable individual power modules, which for example may be 10 kilowatts each and are removable from the overall system without adversely affecting the remaining modules. Each module by means of pulse width modulated switching converts the line AC to DC where it is stored by use of capacitors or a battery and then inverted from DC back to AC. This is done on a three-phase basis without need of any low frequency transformer connection. Common input and output control units provide for the basic pulse width modulated switching signals and other necessary signals.

The efficiency and speed of the system is enhanced by the use of cascode switches, saturable cores in transformers and inductors, and a proportional base drive to the switching transistors.

Claims

1. A power supply for converting single or multi-phase line AC in a regulated manner to a desired single or multi-phase output comprising:

a plurality of substantially identical switched power modules connected in parallel to said AC line and to said output including input switching means switched by pulse width modulated signals for converting AC to DC and output switching means controlled by pulse width modulated signals for converting AC to DC and output switching means controlled by pulse width modulated signals for converting DC to AC; and

input and output control means separate from said power modules for driving said switching means with said pulse width modulated signals whereby any one of said substantially identical switched power modules may be removed from said system without adversely affecting the remaining plurality of switched power modules, said output control means including digital phase locked loop means (PLL) for generating said pulse width modulated switching signal, said PLL including microprocessor means for comparing an output sinusoidal voltage generated by said PLL with an input sinusoidal voltage, and counter and memory means driven by said microprocessor means in accordance with said comparing, for producing said output sinusoidal voltage of a frequency determined by said microprocessor means.

2. A power supply as in claim 1 in which the electrical connection is made between the AC input through the plurality of switched power modules directly to the output without the use of a low frequency transformer coupling.

3. A power supply as in claim 1 where said counter and memory means includes a read only memory containing amplitudes of sine wave at sequential addresses which are addressed by said counter means and a multiplying digital to analog converter means driven by said memory means.

4. A power supply as in claim 3 where said microprocessor means provides a reference output to said multiplying digital to analog converter to determine the amplitude of said output sinusoidal voltage.

5. A power supply as in claim 4, including pulse width modulation signal forming means, including a comparator means comparing said sinusoidal output voltage with the actual AC output voltage of said power supply, the output of said comparator driving said pulse width modulation signal forming means.

6. A power supply as in claim 1 including an energy storage means between said input and output switching means connected between said DC bus and a return line.

7. A power supply as in claim 1 where said microprocessor means is selectively responsive to a said input voltage which is at said line frequency or a nominal frequency and includes means for slewing between said line and nominal frequency.

8. A power supply as in claim 1 where said microprocessor means provides a frequency operating range where if said line frequency goes outside of said range a nominal frequency is locked onto.

9. A power supply as in claim 1 together with a snubber means included in said switching means, including an inductor with a saturated core to minimize energy storage during turn-on.

10. A power supply as in claim 1 where each of said switching means includes cascode connected switches responsive to a single pulse width modulated input signal for providing a switching action.

11. A power supply as in claim 10 where said cascode switches each include a bipolar transistor which is rated at a high voltage and has relatively slow switching speed with its emitter coupled to a field effect transistor rated at a relatively low voltage but with a fast switching speed and providing said single input.

12. A power supply as in claim 10 where said cascode switches include in their input means for controlling the level of turn-on base current for said bipolar transistor.

13. A power supply as in claim 10 where said cascode switches include antisaturation clamp means.

14. A power supply as in claim 10 where said cascode switches include proportional base drive means.

15. A power supply as in claim 14 where said proportional base drive means include transformer means for supplying a proportional base current to said bipolar transistor.

16. A power supply as in claim 15 including means for resetting said transformer means within 10% or less of the period of the frequency of operation of said transformer.

17. A power supply as in claim 16 where said resetting means includes a winding on said transformer and means for applying a reset pulse to said winding for cyclically inverting the magnetic field of said transformer.