Open-loop and closed-loop control method for a three-point converter with active clamped switches, and apparatus for this purpose

• US 6,697,274 B2
• Filed: 03/13/2003
• Issued: 02/24/2004
• Est. Priority Date: 09/13/2000
• Status: Expired due to Term

• Current Assignee: ABB Power Grids Switzerland AG (ABB Limited)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Bernet, Steffen, Brückner, Thomas
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US10/388,022
• Publication Number:
  US 20030165071A1
• Time in Patent Office: 348 Days
• Field of Search: 363/131, 363/132, 363/95, 363/98, 363/97
• US Class Current: 363/132
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters

Abstract

An open-loop and closed-loop control method is proposed for a single-phase or polyphase three-point converter which is connected to a DC voltage intermediate circuit, having two series-connected main switches/inverse diodes between each DC voltage connection and each load connection. The common junction point of the two inner main switches forms the load connection. An active clamped switch with an inverse diode is connected between each common junction point of an inner main switch and an outer main switch and the center tap of the DC voltage intermediate circuit. As a result of which, two possible paths are formed for connecting a load connection to the center tap. Irrespective of the direction of the load current, at least one of the two active clamped switches (T5, T6) is connected to the center tap together with at least one inner main switch for connection of a load connection. The provides a circuit that can carry the current deliberately through the upper path, the lower path, or through both paths, to the center tap during a null state.

Claims

1. An open-loop and closed-loop control method, which comprises:

providing a three-point converter for connecting a DC voltage intermediate circuit having a positive DC voltage connection, a center tap, and a negative DC voltage connection, to three load connections, the three-point converter having;

two series-connected main switches/inverse diodes connected between each of the DC voltage connections and each of the load connections, and

two inner main switches sharing a common junction point, the common junction point forming one of the load connections,

an active clamped switch with an inverse diode connected between each common junction point of an inner main switch and an outer main switch and the center tap to form an upper path and a lower path for connecting respective load connections to the center tap; and

irrespective of a direction of a load current, connecting at least one of the two active clamped switches to the center tap together with at least one of the inner main switches for connecting to one of the load connections, in order to carry the current deliberately through at least one of the upper path and the lower path, to the center tap during a null state.

2. The method according to claim 1, wherein the three-point converter is a single-phase three-point converter.

3. The method according to claim 1, wherein the three-point converter is a polyphase three-point converter.

4. The method according to claim 1, which further comprises, irrespective of the direction of the load current, connecting at least one of the two active clamped switches to the center tap together with at least one of the inner main switches to form a load connection for carrying current deliberately through both the upper path and the lower path, to the center tap during the null state.

5. The open-loop and closed-loop control method according to claim 1, which further comprises commutating one of the outer, positive or negative, DC voltage connections to the center tap by:

initially switching off the outer main switch connected directly to the one of the outer DC voltage connections, the outer main switch lying in a given bridge half, and

connecting a one of the clamped switches in the given bridge half after a dead time.

6. The open-loop and closed-loop control method according to claim 1, which further comprises commutating one of the outer, positive or negative, DC voltage connections to the center tap by:

initially switching off the outer main switch connected directly to the one of the outer DC voltage connections and lying in a first bridge half,

switching on the inner main switch in a second bridge half after a dead time, and

switching off the inner main switch located in the first bridge half after a further dead time.

7. The open-loop and closed-loop control method according to claim 1, which further comprises commutating one of the outer, positive or negative, DC voltage connections to the center tap by:

initially switching off the inner main switch connected to the one of the outer DC voltage connections via one of the outer main switches, the one of the main switches lying in a first bridge half, and

switching on the inner main switch in a second bridge half after a dead time.

8. The open-loop and closed-loop control method according to claim 1, which further comprises:

using semiconductors to form the switches and diodes; and

switching on the active clamped switches as a function of an instantaneous thermal load on the semiconductors.

9. The open-loop and closed-loop control method according to claim 8, which further comprises switching on the active clamped switches such a one of the semiconductors with an instantaneously highest boundary layer temperature is never loaded with switching losses during subsequent commutation.

10. The open-loop and closed-loop control method according to claim 9, which further comprises accounting for the instantaneous thermal load on the semiconductors by forming control signals for the semiconductor switches from switching state commands of a higher-level converter closed-loop control system, phase currents, and boundary layer temperatures of the semiconductors.

11. The open-loop and closed-loop control method according to claim 10, which further comprises:

comparing with each other the boundary layer temperatures of those semiconductors loadable with switching losses as a function of a voltage to be modulated and a direction of a load current during a next commutation to the null state; and

selecting a next null state by not loading a one of the compared semiconductors having a highest boundary layer temperature with switching losses during the next commutation.

12. The open-loop and closed-loop control method according to claim 10, which further comprises calculating online switching and conduction losses as a function of the control signals, of an intermediate-circuit voltage, the phase currents, the boundary layer temperatures, and loss approximations of the semiconductors.

13. The open-loop and closed-loop control method according to claim 12, which further comprises calculating online the boundary layer temperatures as a function of switching and conduction losses, a coolant temperature, and a thermal converter model.

14. An open-loop and closed-loop control apparatus, comprising:

a three-point converter for connecting a DC voltage intermediate circuit having a positive DC voltage connection, a center tap, and a negative DC voltage connection, to three load connections, the three-point converter including;

two series-connected main switches/inverse diodes connected between each of the DC voltage connections and each of the load connections, and

two inner main switches sharing a common junction point, the common junction point forming one of the load connections, and

an active clamped switch with an inverse diode connected between each common junction point of an inner main switch and an outer main switch and the center tap to form an upper path and a lower path for connecting respective load connections to the center tap,

said switches and diodes being semiconductors having phase currents and boundary layer temperatures; and

a modulator producing switching state commands; and

a temperature regulator and automatic drive device for forming control signals for the semiconductor switches from the switching state commands of said modulator, the phase currents, and the boundary layer temperatures of said semiconductors.

15. The open-loop and closed-loop control apparatus according to claim 14, wherein the three-point converter is a single-phase three-point converter.

16. The open-loop and closed-loop control apparatus according to claim 14, wherein the three-point converter is a polyphase three-point converter.

17. The open-loop and closed-loop control apparatus according to claim 14, further comprising:

a component for storing semiconductor loss approximations and emitting stored semiconductor loss approximations as signals; and

an online calculation having an input side and an output side and receiving, on said input side, the control signals for said semiconductor switches, the boundary layer temperatures of said semiconductors, the phase currents, an intermediate-circuit voltage, and the signals from said component, and emitting calculated switching and conduction losses on said output side.

18. The open-loop and closed-loop control apparatus according to claim 17, further comprising:

a thermal converter model emitting signals; and

a further online calculation having an input side and an output side, receiving, on said input side, signals from said online calculation, a coolant temperature, and the signals from a thermal converter model, and emitting the boundary layer temperatures of said semiconductors on said output side.