Inverter inrush current limiting

• US 10,128,774 B2
• Filed: 07/10/2015
• Issued: 11/13/2018
• Est. Priority Date: 05/08/2011
• Status: Active Grant

• Current Assignee: Koolbridge Solar, Inc.
• Original Assignee: Koolbridge Solar, Inc.
• Inventors: Dent, Paul Wilkinson
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): Quddus, Nusrat
• Application Number:
  US14/797,039
• Publication Number:
  US 20150318796A1
• Time in Patent Office: 1,222 Days
• Field of Search: 363 16, 363 17, 363 36, 363 37, 363 39- 41, 363 55- 5605, 363 97, 363 98, 363131-134, 363165
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105
• CPC Class Codes: H02J 2300/00 Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
• CPC Class Codes: H02J 2300/22 The renewable source being solar energy
• CPC Class Codes: H02J 3/00 Circuit arrangements for ac mains or ac distribution networks
• CPC Class Codes: H02J 3/007 Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing uninterruptable power supply H02J9/00
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02A 30/00 Adapting or protecting infrastructure or their operation
• CPC Class Codes: Y02B 10/10 Photovoltaic [PV]
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A method and circuit arrangement is described for start-up and shut-down of high power DC to AC inverters which limits inrush current for capacitor charging, reduces input and output relay contact stress and discharges internal capacitors upon shut down. A preferred inrush limiting component has a higher resistance when hot than when cold, such as an incandescent filament lamp.

Claims

1. A DC to AC inverter having a circuit arrangement for limiting capacitor inrush current and fault currents and reducing electrical sparking at relay contacts, comprising:

a control processor for performing a predetermined sequence of start-up or shut-down steps;

DC to AC conversion circuitry controllable to be activated or deactivated by said control processor by enabling or disabling transistor switching;

input terminals for the connection of a DC power source;

output terminals for outputting AC power from said DC to AC conversion circuitry;

at least one output relay having at least one set of normally open contacts for connecting the output of said DC to AC conversion circuitry to said output terminals, said at least one output relay being controllable by said control processor;

a main power relay having at least one set of normally open contacts for connecting said DC power source from said input terminals to said DC to AC conversion circuitry, said main power relay being controllable by said control processor;

a start-up relay having at least one set of normally open contacts connected in series with an incandescent filament lamp, the series combination being connected in parallel with said at least one set of normally open contacts of said main power relay, said start-up relay being controllable by said control processor, and

a photodetector placed adjacent to said incandescent filament lamp for providing an indication to said control processor of whether said lamp is lit.

2. The DC to AC inverter of claim 1, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry to start attempting to convert DC power to AC power before a DC power input is applied via said main power relay or start-up relay.

3. The DC to AC inverter of claim 1, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition;

STEP 2;

Activating said DC to AC conversion circuitry to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay, and

STEP 3;

Controlling said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry through said incandescent filament lamp in order to limit any inrush or fault current to the magnitude of current passed by said incandescent filament lamp.

4. The DC to AC inverter of claim 1, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry in order to start up said DC to AC inverter according to a sequence including the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition;

STEP 2;

Activating said DC to AC conversion circuitry to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay;

STEP 3;

Controlling said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry through said incandescent filament lamp in order to limit any inrush or fault current to the current passed by said incandescent filament lamp;

STEP 4;

Monitoring the output of said photodetector to determine that said incandescent filament lamp lit momentarily and then extinguished within a predetermined period of time, and

STEP 5;

If and when the conditions in step 4 are fulfilled, controlling said main power relay to close its contacts, else if the conditions in step 4 are not fulfilled, controlling said start-up relay to the open condition and aborting start-up.

5. The DC to AC inverter of claim 1, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition;

STEP 2;

Activating said DC to AC conversion circuitry to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay;

STEP 3;

controlling said start-up relay and main power relay to apply DC power to the input of said DC to AC conversion circuitry;

STEP 4;

Temporarily deactivating said DC to AC conversion circuitry by disabling said transistor switching;

STEP 5;

Controlling said at least one output relay to the contact closed condition, and

STEP 6;

Re-activating said DC to AC conversion circuitry by re-enabling transistor switching.

6. A safe start-up and shut-down circuit arrangement for use with a high power DC to AC inverter for converting power from a DC power source to AC power at an AC output, comprising:

A control processor for performing a predetermined sequence of start-up or shut-down steps;

DC to AC conversion circuitry including a DC-to-DC converter, said DC to AC conversion circuitry and said DC-to-DC converter being controllable to be activated or deactivated by said control processor by enabling or disabling transistor switching;

a main power relay having normally open contacts connected between a first polarity terminal of said DC power source and a corresponding polarity DC input of said DC to AC converter circuitry and said DC-to-DC converter, the main power relay contacts being controlled to open or close by said processor;

a double-throw start-up relay having a normally open contact, a normally closed contact and a common contact, the contacts being connected such that when the relay is energized, DC current flows from said first polarity DC power power source terminal through an incandescent filament lamp to said corresponding polarity DC input of said DC to AC converter circuitry and said DC-to-DC converter, and when the relay is not energized, said corresponding first polarity DC input of said DC to AC conversion circuitry and said DC-to-DC converter is connected through an incandescent filament lamp to the DC power source terminal of opposite polarity to said first polarity, the start-up relay being controlled by said processor;

at least one output relay having normally open contacts for connecting the AC output of said DC to AC conversion circuitry to a load, the at least one output relay being controlled by said processor, and

photodetection circuitry to provide an indication to said control processor of whether an incandescent filament lamp connected to said double-throw start-up relay is lit or not lit.

7. The DC to AC inverter of claim 6, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied via said main power relay or start-up relay.

8. The DC to AC inverter of claim 6, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay, and

STEP 3;

Energizing said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while limiting any inrush or fault current to incandescent filament lamp current.

9. The DC to AC inverter of claim 6, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay;

STEP 3;

Controlling said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while limiting any inrush or fault current to incandescent filament lamp current;

STEP 4;

Monitoring the indication provided by said photodetection circuitry to determine that a lamp-lit indication was detected followed by a lamp-extinguished detection within a predetermined period of time, and

STEP 5;

If and when the conditions in step 4 are fulfilled, controlling said main power relay to close its contacts, else if the conditions in step 4 are not fulfilled, controlling said start-up relay to the open condition and aborting start-up.

10. The DC to AC inverter of claim 6, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied via said main power relay or start-up relay;

STEP 3;

controlling said start-up relay and main power relay to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while limiting inrush current to that of an incandescent filament lamp;

STEP 4;

Temporarily deactivating said DC to AC conversion circuitry by disabling its transistor switching;

STEP 5;

Controlling said at least one output relay to the contact closed condition, and

STEP 6;

Re-activating said DC to AC conversion circuitry by re-enabling its transistor switching.

11. The DC to AC inverter of claim 6, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to shut down said DC to AC inverter according to a predetermined sequence including at least the following steps;

STEP 1;

Deactivating said DC to AC conversion circuitry by disabling its transistor switching;

STEP 2;

De-energizing said at least one output relay and said main power relay to the contact open condition;

STEP 3;

De-energizing said start-up relay while monitoring the indication from said photodetection circuitry;

STEP 4;

Determining that said photodetection circuitry provided a lamp-lit indication followed by a lamp-extinguished indication within a predetermined time period after de-energizing said start-up relay, and

STEP 5;

Deactivating said DC to DC converter by disabling its transistor switching after said predetermined time period.

12. A safe start-up and shut-down circuit arrangement for use with a high power DC to AC inverter, comprising:

A control processor for performing a predetermined sequence of start-up or shut-down steps, including enabling or disabling transistor switching within said DC to AC converter circuitry;

DC to AC conversion circuitry including a DC-to-DC converter, said DC to AC conversion circuitry and said DC-to-DC converter being controllable to be activated or deactivated by said control processor by enabling or disabling transistor switching;

a main power relay having normally open contacts connected between a first polarity terminal of a DC power source and a corresponding polarity DC input of said DC to AC converter circuitry and said DC-to-DC converter, the main power relay contacts being controlled to open or close by said processor;

a double-throw start-up relay having a normally open contact, a normally closed contact and a common contact, the contacts being connected such that when the relay is energized, DC current flows from said first polarity DC power power source terminal through a current limiting device to said corresponding polarity DC input of said DC to AC converter circuitry and said DC-to-DC converter, and when the relay is not energized, said first corresponding DC input of said DC to AC conversion circuitry and said DC-to-DC converter is connected through a current limiting device to the DC power source terminal of opposite polarity to said first polarity, the start-up relay being controlled by said processor;

at least one output relay having normally open contacts for connecting the AC output of said DC to AC conversion circuitry to a load, the at least one output relay being controlled by said processor, and

current indication circuitry to provide indications to said control processor of whether any current limiting device connected to said double-throw start-up relay is passing current greater or less than predetermined thresholds.

13. The DC to AC inverter of claim 12, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay.

14. The DC to AC inverter of claim 12, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay, and

STEP 3;

Controlling said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while constraining the magnitude of any inrush or fault current by a current limiting device.

15. The DC to AC inverter of claim 12, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay;

STEP 3;

Controlling said start-up relay to close its contacts in order to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while constraining the magnitude of any inrush or fault current by a current limiting device;

STEP 4;

Monitoring the current indication provided by said current indication circuitry to determine that the current in a current limiting device first exceeded a predetermined threshold and then fell below a predetermined threshold within a predetermined period of time, and

STEP 5;

If and when the conditions in step 4 are fulfilled, controlling said main power relay to close its contacts, else if the conditions in step 4 are not fulfilled, controlling said start-up relay to the open condition and aborting start-up.

16. The DC to AC inverter of claim 12, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to start up said DC to AC inverter according to a sequence including at least the following steps;

STEP 1;

Ensuring that all relays are initially in the open condition, and

STEP 2;

Activating said DC to AC conversion circuitry and said DC-to-DC converter to start attempting to convert DC power to AC power before a DC input is applied from said main power relay or start-up relay;

STEP 3;

controlling said start-up relay and main power relay to apply DC power to the input of said DC to AC conversion circuitry and said DC-to-DC converter while constraining the magnitude of any inrush or fault current by a current limiting device;

STEP 4;

Temporarily deactivating said DC to AC conversion circuitry by disabling its transistor switching;

STEP 5;

Controlling said at least one output relay to the contact closed condition, and

STEP 6;

Re-activating said DC to AC conversion circuitry by re-enabling its transistor switching.

17. The DC to AC inverter of claim 12, further including:

Software for execution on said processor configured to control said start-up relay, said main power relay, said at least one output relay and the activation and deactivation of said DC to AC conversion circuitry and said DC-to-DC converter in order to shut down said DC to AC inverter according to a predetermined sequence including at least the following steps;

STEP 1;

Deactivating said DC to AC conversion circuitry by disabling its transistor switching;

STEP 2;

De-energizing said at least one output relay and said main power relay to the contact open condition;

STEP 3;

De-energizing said start-up relay while monitoring the indication from said current indication circuitry;

STEP 4;

Determining that said current indication circuitry provided an indication that current in a current limiting device first exceed a predetermined threshold and then fell below a predetermined threshold within a predetermined period of time after de-energizing said start-up relay, and

STEP 5;

Deactivating said DC to DC converter by disabling its transistor switching after said predetermined time period.

18. The DC to AC inverter of claim 12 in which the term “

a current limiting device”

can include a device having an electrically resistive element having a much greater resistance when the temperature of the resistive element is high than when the temperature of the resistive element is low.