WO2012152831A1

WO2012152831A1 - Bay controller with integrated point-on-wave controller

Info

Publication number: WO2012152831A1
Application number: PCT/EP2012/058537
Authority: WO
Inventors: Michael Stanek; Andrjia DJURDJIC
Original assignee: Abb Technology Ag
Priority date: 2011-05-09
Filing date: 2012-05-09
Publication date: 2012-11-15
Also published as: EP2707957A1; CN103548267A

Abstract

A bay controller (1) for the monitoring and control of a bay (97) in a power transmission network (98) is disclosed. The bay controller (1) according to the invention includes both classical bay controller functionality and point-on-wave (POW) control of circuit breaker switching operations in the bay (97) of the power transmission network (98). For this, a POW-capable interface (6) to the circuit breaker device (2) as well as an improved control unit (7, 7a, 7b) is integrated into the bay controller (1). By providing a bay controller (1) with integrated point-on-wave control functionality, costs are reduced and reliability is increased. Furthermore, improved operation strategies are possible for both the bay control as well as the point-on-wave control functionality due to the shared access to the full information about the operating parameters of the bay (97) in the power transmission network (98).

Description

Bay controller with integrated point-on-wave controller

Technical Field

The present invention relates to a bay con^¬ troller device with integrated point-on-wave controller functionality that monitors and controls the operation of a bay, particularly in an AC power transmission network. It furthermore relates to a bay in a power transmission network comprising a circuit breaker device and a bay controller with integrated point-on-wave controller func^¬ tionality.

Introduction and Background Art

A bay controller controls the switchgear and monitors the operation within a bay in a power transmis^¬ sion network. Traditionally, switching actions, e.g. by circuit breakers, are executed immediately after recep^¬ tion of a switching command. In many instances, however, switching transients can be reduced significantly by closing and opening circuit breaker devices (CBs) under point-on-wave (POW) control (also called "synchronous switching" or "controlled switching") . In short, POW control is to delay the CB operation in such a way that con^¬ tact touch/separation and/or start/stop of current flow will occur at a point in time that is well suited for the CB, the switched load, the bay, and/or the whole network. This point in time is usually chosen as a specific phase angle of a reference current or voltage (operating param^¬ eter) in the bay and/or the network; as an example, ca- pacitive loads are usually switched at an instant when the reference voltage is zero, i.e. at a zero crossing of the (usually sinusoidal) network voltage. The POW con^¬ troller acquires the reference current or voltage via monitoring signals from monitoring devices, such as volt- age sensors or current sensors, at an appropriate moni^¬ toring interface on the POW controller.

Traditionally, POW control functionality is provided by a stand-alone device (POW controller) that receives arbitrarily timed external switching commands from a bay controller and issues precisely timed circuit breaker switching commands to the CB .

A conventional POW controller has means for acquiring reference voltage signals, current signals, bi^¬ nary signals, and/or additional sensor signals for poten^¬ tial deviation compensation, and/or it has means for accurately releasing the CB, usually each CB pole individu^¬ ally. Furthermore, POW controllers according to prior art are triggered by one or more external switching commands from switching command issuing devices, e.g. bay control^¬ lers .

The described implementations have the disad^¬ vantage, however, that appropriate switching strategies of the CB may not be achieved in all possible cases due to missing information about the CB status and/or the operating parameters of the power transmission network in the bay controller and/or in the POW controller.

US 2009/0073627 discloses a method and appa^¬ ratus for optimizing synchronous switching operations in power systems. Switching commands, which were beforehand issued from a higher-level unit such as a bay controller, are received by the synchronous switching apparatus and are therein used to calculate delayed optimized synchro^¬ nous switching times. However, the synchronous switching apparatus cannot perform bay controller functionality, such as monitoring and controlling status and activity of a plurality of primary bay devices, issuing switching commands, and the like. In particular, the synchronous switching apparatus does not monitor or control any dis^¬ connector, earthing switch, or load switch of the bay. Instead, it is only assigned to a single circuit breaker which requires synchronous switching signals. Disclosure of the Invention

Hence it is a general objective of the pre^¬ sent invention to provide a device and a bay that at least partly overcome these disadvantages.

These objectives are achieved by the device and the bay of the independent claims. Embodiments are disclosed in the dependent claims and claim combinations.

Accordingly, a bay controller for control and monitoring of a bay with a housing, a power supply, a control interface, a parameter input interface, a CB in^¬ terface, and a control unit is provided. On the one hand, classical bay controller functionality, i.e. the control and monitoring of the operation of a bay in a power transmission network by controlling and monitoring the active and/or passive elements in said bay is provided by the device according to the invention.

The bay controller's control interface (e.g. a human-machine-interface comprising a touch-screen with I/O functionality for a user and/or a computer interface and/or a standardized interface for connections to other bay controllers, protection devices, and/or higher- hierarchy controllers in the power transmission network) provides I/O and connection functionality, while the pa^¬ rameter input interface of the bay controller is adapted to monitor operating parameters in the power transmission network via connections to monitoring devices and/or pas^¬ sive elements (e.g. voltage monitoring devices, current monitoring devices, binary monitoring devices) . The control unit of the bay controller is adapted to monitor op^¬ eration of the bay in the power transmission network and to calculate and execute a first operation strategy for said bay, e.g. making a decision when to open and/or close the CB and/or other switching elements such as load switches in the bay.

The functionality of the bay controller in detail may typically be such that: said control interface is adapted to receive control signals from an operator and/or a second control^¬ ler device and to provide status and/or control signals to an operator and/or to said second controller device, said parameter input interface comprises mon^¬ itoring interfaces to monitoring devices in said power transmission network and is adapted to monitor at least one operating parameter of said power transmission network via monitoring signals from said monitoring devices, said control unit is connected to said power supply, said control interface, and said parameter input interface, and wherein said control unit is adapted to monitor the operation of said bay in said power transmis^¬ sion network and to calculate a first operation strategy for at least one primary bay device of said bay in said power transmission network, which primary bay device is not a circuit breaker device.

Now, by introducing a POW-capable interface to the CB and integrating POW functionality into the con^¬ trol unit of the bay controller according to the invention, several advantages arise: First, additional inter^¬ faces from a prior art bay controller to a separate prior art POW controller as well as other wiring efforts become unnecessary, thus reducing costs and increasing reliability. Second, by using an integrated device instead of two separate devices, demand for space is reduced. Third, the bay controller has access to all the information (operat^¬ ing parameters of the power transmission network) of the POW controller. Fourth, vice versa, the POW controller functionality has access to all the information (operat^¬ ing parameters of the power transmission network) of the bay controller.

In an embodiment, the bay controller is adapted to issue at least one network-asynchronous sig^¬ nal, in particular asynchronous switching command signal, to the primary bay device. In another embodiment, the primary bay device is a disconnector, an earthing switch, or a load switch.

In another embodiment, the bay controller furthermore comprises a CB interface, which is adapted to be connected to said control unit and to said circuit breaker device in said bay of said power transmission network and to issue a circuit breaker network- synchronous switching command to said circuit breaker de^¬ vice .

In another embodiment, said control unit is furthermore adapted to calculate a second operation strategy for point-on-wave controlling of said circuit breaker device in said bay based on said operating parameters of said power transmission network. Thus, improved (first and second) operation strategies for both said bay in the power transmission network and said circuit breaker device can be achieved.

In another embodiment, the control unit of the bay controller is adapted to calculate said second operation strategy for more than one circuit breaker and/or other switching elements, e.g. such as load switches in said bay. Thus, the synchronous switching of more than one circuit breaker device is possible.

In another embodiment, said control unit is adapted to calculate additionally a second operation strategy for point-on-wave controlling of the circuit breaker device for network-synchronous fault current in^¬ terruption .

In another embodiment, said control inter^¬ face, said parameter input interface, said CB interface, and said control unit are arranged commonly in said hous^¬ ing, in particular that phase-precision output signals of the point-on-wave controller are provided from the bay controller housing.

In another embodiment, the housing of the bay controller is adapted to be mountable in a rack, e.g. a 19-inch rack, e.g. of a local control cabinet. Thus, ex^¬ isting infrastructure can be used and costs are reduced.

In another embodiment, the bay controller and the point-on-wave controller are connected to the same power supply and/or same control interface and/or same parameter input interface and/or same control unit.

In another embodiment, at least a subset of monitoring signals collected by the bay controller are used both for bay controlling and for point-on-wave controlling .

In another embodiment, the control unit of the bay controller comprises a central processing unit (CPU) and a memory. Thus, the monitoring and control of the bay and the POW functionality can be advantageously implemented as software (modules) in said control unit. Then, in another embodiment, the software code can be up^¬ dated, e.g. by attaching an external drive or PC, e.g. via USB or Ethernet, to said control interface, to pro^¬ vide additional functionality and/or to fix bugs.

The current invention also relates to a bay comprising at least one bay controller as disclosed here^¬ in .

In particular, a bay is disclosed in a power transmission network that comprises at least one circuit breaker device, a plurality of monitoring devices, and at least one bay controller with integrated POW control functionality. Due to the shared information about the operating parameters in the bay of the power transmission network, improved first and second operation strategies are achieved both for the CB and the whole bay.

In an embodiment, no separate external POW controller needs to be used due to the integrated POW functionality in the bay controller. Thus, wiring effort is reduced and reliability and functionality are im^¬ proved .

In an embodiment, a single bay controller provides POW control for more than one CB or load switch or other switch in the bay of the power transmission network. Thus, multiple switching elements can be used in synchronous switching mode without utilizing a separate POW controller for each switching element.

In general, the current invention can be im^¬ plemented as a device and/or method.

Brief Description of the Drawings

The invention will be better understood and objectives other than those set forth above will become apparent when consideration is given to the following detailed description of the invention. This description makes reference to the annexed drawings, wherein:

Fig. 1 (prior art) shows a bay with a CB in a power transmission network with a bay controller and a separate POW controller, and

Fig. 2 shows an embodiment of the bay with a CB in a power transmission network with a bay controller with integrated POW functionality.

Modes for Carrying Out the Invention Summary:

A bay controller for the monitoring and control of a bay in a power transmission network is disclosed. The bay controller according to the invention includes both classical bay controller functionality and point-on-wave (POW) control of circuit breaker switching operations in the bay of the power transmission network. For this, a POW-capable interface to the circuit breaker device as well as an improved control unit is integrated into the bay controller. By providing a bay controller with integrated point-on-wave control functionality, costs are reduced and reliability is increased. Further^¬ more, improved operation strategies are possible for both the bay control as well as the point-on-wave control functionality due to the shared access to the full infor^¬ mation about the operating parameters of the bay in the power transmission network.

Definitions :

A bay is the part of a substation within which the switchgear and control gear relating to a given circuit are contained. Usually it comprises a circuit breaker with its associated disconnectors, earthing switches, instrument transformers, and/or control & pro^¬ tection equipment.

A bay controller is the external interface to control functions in a bay within a substation in a power transmission network. It controls the active elements e.g. circuit breaker or switching device, and monitors the operation (i.e. by monitoring passive elements such as voltage monitoring devices, current monitoring devic^¬ es, binary monitoring devices, etc.) within the bay. Also, it interfaces with neighboring bays, e.g. for inter^¬ locking. Thus, a bay controller has access to a plurality of control, status, and monitoring information signals in a bay. The bay controller controls and monitors typically several or preferably all switchgears in the bay. In par^¬ ticular it ensures proper operation, and issues alarms in case of problems. It provides interlocking functionality to prevent dangerous or damaging switching operations and to assure personnel safety. It usually also keeps a log of events in the bay. Furthermore, it may include ad^¬ vanced functions such as network synchronization, auto- reclosing, voltage control, and/or protection, e.g. breaker failure protection.

A circuit breaker (CB) device is a switching device designed to make, carry, and interrupt load and fault currents. It opens or closes a single phase or three phases in a circuit within the power transmission network, advantageously synchronized to a suitable oper^¬ ating parameter (reference signal such as reference cur- rent or voltage) in the power transmission network (point-on-wave control of the CB) . The energy for the ac^¬ tual execution of a switching action by an actuator is stored, e.g. mechanically in a spring, pneumatically in a gas reservoir of the CB drive, or electrically in a ca^¬ pacitor. When a switching action is to be performed, the energy is mechanically, hydraulically, and/or electrical^¬ ly transmitted to the poles of the CB device. A suitable replenishing device such as electrical recharger, hydraulic pump, or pneumatic pump replenishes the energy after such a switching action. The operating time for a switching action may depend on the level of stored energy.

The term "high-voltage" relates to voltages larger than 1 kV, in particular larger than 72 kV.

Description of the Figures :

Fig. 1 shows a bay 97 with a CB 2 in a power transmission network 98 with a bay controller 1 and a separate POW controller 99 according to prior art. The bay controller 1 comprises a housing 3a, a power supply 4a, a control interface 5a, a parameter input interface 8a, and a control unit 7a (comprising a central pro^¬ cessing unit 7al and memory 7a2) . Furthermore, it moni^¬ tors operating parameters (e.g. voltages, currents, the status of the CB 2, and/or binary states of other switching elements not shown) via its parameter input interface 8a, specifically via monitoring signals 89 from monitor^¬ ing devices 9a, 9b in the bay 97 and/or in the power transmission network 98. Furthermore, the bay controller 1 comprises a binary output 96 through which an external switching command 94 is sent to the POW controller 99, specifically to its binary input 95, if the CB 2 is to be operated. This external switching command 94 is usually arbitrarily timed, i.e. is not synchronized to the oper^¬ ating parameters in the power transmission network 98.

The POW controller 99 comprises a separate housing 3b, a separate power supply 4b, a separate con- trol interface 5b, a separate parameter input interface 8b, and a separate control unit 7b (comprising a central processing unit 7bl and a memory 7b2) . The POW controller 99 receives said external switching command 94 through its binary input 95 and calculates an operation strategy for the CB 2 depending on independently monitored operat^¬ ing parameters (e.g. voltages, currents, or binary states of switching elements such as load switches; via its pa^¬ rameter input interface 8b) of the bay 97 and/or the pow^¬ er transmission network 98. In other words, a control unit 7b of the POW controller 99 computes the operation strategy for the CB 2 and issues a precisely timed CB switching command 93 through its CB interface 6 of the POW controller 99 when the CB 2 is to be closed or opened. Thus, synchronous switching is achieved. However, since the POW controller 99 does usually not have access to all the information about the operating parameters of the power transmission network 98, well suited operation strategies are not always achieved.

Fig. 2 shows a bay 97 with a CB 2 in a power transmission network 98 with a bay controller 1 with integrated POW functionality according to an embodiment of the present invention. The bay controller 1 with POW functionality comprises one single housing 3, power sup^¬ ply 4, control interface 5, parameter input interface 8, and control unit 7 (comprising a central processing unit 71 and a memory 72) . Connectivity (for status/control signals 24) of the bay controller 1 is provided through a control interface 5, e.g. comprising a touch-screen with I/O functionality for a user 22 and/or a computer interface for connections to an external computer 23 and/or a standardized interface for connections to other bay con^¬ trollers 1 and/or protection equipment and/or higher- hierarchy controllers in the power transmission network 98. The bay controller 1 monitors operating parameters (e.g. voltages, currents, the status of the CB 2, and/or binary states of other switching elements such as load switches) via its parameter input interface 8, specifi^¬ cally via monitoring signals 89 from monitoring devices 9a, 9b in the bay 97 and/or the power transmission network 98 that are acquired by monitoring interfaces 81, 82 of the parameter input interface 8.

Furthermore, the bay 97 comprises at least one primary device 20, 21, which is in addition to and different from the circuit breaker device 2 and can e.g. be a disconnector 20 or an earthing switch 21. Such primary device 20, 21 is connected to the control unit 7 via control and monitoring lines 90 and is operated by the control unit 7 with at least one network-asynchronous switching command signal.

Monitoring and control of the bay 97 as well as POW control of the CB 2 are all carried out by the common control unit 7, advantageously by software modules that run on the central processing unit 71 of the control unit 7. When the CB 2 shall be closed or opened, a pre^¬ cisely timed CB switching command 93 is sent directly to the CB 2 via the CB interface 6 of the bay controller 1. Thus, both the bay controller 1 and the integrated POW functionality have direct access to all the information about operating parameters in the bay 97 and/or the power transmission network 98.

Therefore improved operation strategies are achieved in many cases. E.g., if the bay controller 1 controls a hydraulic pump 2a that - after a switching command by the CB 2 has been executed - replenishes the stored energy (e.g. the pressure in a hydraulic reservoir 2b) for the actuator 2c of the CB 2 via control/monitoring signals 92, the POW functionality can use this infor^¬ mation for optimizing its estimation of the operating times of the CB 2. Another approach would be to use, e.g., an electromagnetic actuator and a capacitor as en^¬ ergy reservoir. Hydraulic pressure or charge level of the respective reservoir are measured and transmitted to the bay controller 1 by monitoring signal 92 and - depending on the stored energy - more precise operating times of the CB 2 switching action can be estimated by the POW functionality of the bay controller 1.

Additionally, information on the binary states of other CBs 2 and/or other switching elements within the bay 97 and/or in other bays may be used to se^¬ lect the operation strategy for the CB 2. Having the POW functionality running on the same control unit 7 as all other bay controller functions makes the initiation of a POW controlled operation of the CB 2 faster compared to the prior-art configuration with separate devices, be^¬ cause the entire signal chain between the two separate prior-art control units 7a and 7b is omitted. For the same reason the system is more reliable, i.e. more immune against errors that might have been introduced in the signal links between the two separate prior-art control units 7a and 7b.

On the hardware and/or software side of the bay controller 1, a bay controller 1 according to the present invention comprises:

* A CB interface 6 comprising precision binary outputs with sufficient accuracy for point-on-wave control for each CB pole, and

* software that runs on the central pro^¬ cessing unit 7a of the control unit 7 of the bay control^¬ ler 1 and comprises POW functionality.

As a further embodiment, protection trip commands could also be passed to the POW software module of the bay controller 1. Then, an appropriate additional se^¬ cond operation strategy and algorithm for controlled net^¬ work-synchronous fault current interruption is implement^¬ ed; this second operation strategy differs from the ones that are used during regular operation conditions. There^¬ fore, such a finely tuned operation strategy is not pos^¬ sible with a classical separate-control-devices- configuration . Notes :

The term "binary" with regard to a two-state or on-off state system is used synonymous to "1-bit- digital" or simply "digital".

The parameter input interfaces and related monitoring signals and monitoring devices can be designed and/or operated as digital or analog devices, independent of the type of information that is processed and/or moni^¬ tored by/via them. In other words, the analog and/or bi^¬ nary operating parameter (s) of the power transmission network can be transmitted, e.g., as digital data over a digital communication interface.

Reference numbers

1 : bay controller

2 : circuit breaker

2a : replenishing device

2b: reservoir

2c : actuator

3, 3a, 3b: housing

4, 4a, 4b: power supply

5, 5a, 5b: control interface

6: CB interface

7, 7a, 7b: control unit

71, 7al, 7bl : central processing unit

72, 7a2, 7b2 : memory

8, 8a, 8b: parameter input interface

9a, 9b: monitoring devices

20: disconnector

21: earthing switch

22 : operator

23: computer

24: status/control signals

81, 82: monitoring interfaces

89: monitoring signals

90: control/monitoring lines or signals

92: control/monitoring signals

93: CB switching command

94 : external switching command

95: binary input

96: binary output

97: bay

98: power transmission network

99: external point-on-wave controller

(prior art) .

Claims

1. Bay controller (1) for control and monitoring of a bay (97), in particular in an AC high-voltage power transmission network (98), comprising a housing (3), a power supply (4), a control interface (5), a pa^¬ rameter input interface (8) and a control unit (7), wherein

said control interface (5) is adapted to re^¬ ceive control signals (24) from an operator (22, 23) and/or a second controller device (1) and to provide sta^¬ tus and/or control signals (24) to an operator (22, 23) and/or to said second controller device (1),

said parameter input interface (8) comprises monitoring interfaces (81, 82) to monitoring devices (9a, 9b) in said power transmission network (98) and is adapted to monitor at least one operating parameter of said power transmission network (98) via monitoring signals (89) from said monitoring devices (9a, 9b),

said control unit (7) is connected to said power supply (4), said control interface (5), and said parameter input interface (8), and wherein said control unit (7) is adapted to monitor the operation of said bay (97) in said power transmission network (98) and to calculate a first operation strategy for at least one prima^¬ ry bay device (20, 21) of said bay (97) in said power transmission network (98), which primary bay device (20, 21) is not a circuit breaker device (2),

characterized in that the bay controller (1) includes a point-on-wave controller for controlling net^¬ work-synchronous operation of at least one circuit break^¬ er device (2) in said bay (97) .

2. Bay controller (1) of claim 1, wherein the bay controller (1) is adapted to issue at least one net^¬ work-asynchronous signal, in particular switching command signal, to the primary bay device (20, 21) .

3. Bay controller (1) of any of the preceding claims, wherein the primary bay device (20, 21) is a dis^¬ connector (20), an earthing switch (21), or a load switch .

4. Bay controller (1) of any of the preceding claims, furthermore comprising a CB interface (6), which is adapted to be connected to said control unit (7) and to said circuit breaker device (2) in said bay (97) of said power transmission network (98) and to issue a circuit breaker network-synchronous switching command (93) to said circuit breaker device (2) .

5. Bay controller (1) of any of the preceding claims, wherein said control interface (5) , said parame^¬ ter input interface (8), said CB interface (6), and said control unit (7) are arranged commonly in said housing (3) , in particular that phase-precision output signals of the point-on-wave controller are provided from the bay controller housing (3) .

6. Bay controller (1) of any of the preceding claims, characterized in that the bay controller (1) and the point-on-wave controller are connected to the same power supply (4) and/or same control interface (5) and/or same parameter input interface (8) and/or same control unit ( 7 ) .

7. Bay controller (1) of any of the preceding claims, characterized in that at least a subset of moni^¬ toring signals collected by the bay controller (1) are used both for bay controlling and for point-on-wave controlling .

8. Bay controller (1) of any of the preceding claims, characterized in that said control unit (7) is furthermore adapted to calculate a second operation strategy for point-on-wave controlling of said circuit breaker device (2) in said bay (97) based on said operat^¬ ing parameters of said power transmission network (98) .

9. Bay controller (1) of claim 8, comprising more than one CB interface (6) wherein said control unit (7) is adapted to calculate a plurality of second opera^¬ tion strategies for point-on-wave controlling of more than one circuit breaker device (2) in said bay (97) .

10. Bay controller (1) of claim 8 or 9, wherein said control unit (7) is adapted to calculate an additional second operation strategy for point-on-wave controlling of the circuit breaker device (2) for network-synchronous fault current interruption.

11. Bay controller (1) of any of the preced^¬ ing claims, wherein said housing (3) is adapted to be rack-mountable, in particular in a 19-inch-rack .

12. Bay controller (1) of any of the preceding claims, wherein said control unit (7) comprises a central processing unit (71) and a memory (72) .

13. Bay controller (1) of claim 8 and 12, wherein said central processing unit (71) is adapted to execute software code that is stored in said memory (72) to calculate said first operation strategy for said bay (97) in said power transmission network (98) and said second operation strategy for point-on-wave controlling of said circuit breaker device (2) based on said operating parameters of said power transmission network (98) .

14. Bay controller (1) of claim 13, wherein said software code is updateable, in particular via said control interface (5) .

15. Bay controller (1) of any of the preced^¬ ing claims, which is adapted to monitor an energy level stored in a reservoir (2b) for the actuator (2c) of said circuit breaker device (2), wherein said second operation strategy for said circuit breaker device (2) is based on said energy level.

16. Bay controller (1) of claim 15, wherein said reservoir (2b) and said actuator (2c) comprise pneu^¬ matic and/or hydraulic and/or mechanical components.

17. Bay controller (1) of any of the claims 15-16, wherein said reservoir (2b) and/or said actuator (2c) comprise (s) electrical and/or electromagnetic compo^¬ nents .

18. Bay (97) in a power transmission network (98), the bay comprising at least one bay controller (1) of any of the preceding claims.

19. Bay according to claim 18, being adapted for network-synchronous operation of a circuit breaker device (2) and comprising at least one circuit breaker device (2), and being adapted for network-asynchronous operation of a primary bay device (20, 21) different from the circuit breaker device (2) and comprising at least one such primary bay device (20, 21) .

20. Bay (97) according to claim 18 or 19, wherein said bay (97) does not comprise a separate exter^¬ nal point-on-wave controller (99).

21. Bay (97) in a power transmission network (98) of any of the claims 18-20, comprising at least two circuit breaker devices (2), wherein said bay controller (1) comprises more than one CB interface (6) and wherein said control unit (7) of said bay controller (1) is adapted to calculate a plurality of second operation strategies for point-on-wave controlling of more than one circuit breaker device (2) in said bay (97) .

22. Bay (97) in a power transmission network (98) of claim 21, comprising exactly one said bay con^¬ troller ( 1 ) .