WO2015145307A1

WO2015145307A1 - Frequency converter with intermediate circuit and method for the reduction of power consumption of intermediate circuit of frequency converter that is in stand-by mode, and elevator

Info

Publication number: WO2015145307A1
Application number: PCT/IB2015/051990
Authority: WO
Inventors: Esa Putkinen
Original assignee: Kone Corporation
Priority date: 2014-03-25
Filing date: 2015-03-18
Publication date: 2015-10-01
Also published as: FI20145271L

Abstract

A frequency converter (1) with an intermediate circuit (13) for driving a motor (M) comprises a rectifier (11), an inverter (12) and a direct-current intermediate circuit (13) between these, which direct-current intermediate circuit (13) comprises at least one capacitor bank (18, 19) comprising a balancing resistor (16, 17) for equalising the voltage (U_C) over the direct-current intermediate circuit (13) in the operating situation of the motor (M). Moreover, the frequency converter (1) comprises a charging circuit (34, 44) which is connected or connectable to the direct-current intermediate circuit (13) for supplying a float voltage (U_L )to the direct-current intermediate circuit (13) when the switch (2, 3, 4) is open in order to keep the frequency converter (1) in the stand-by mode. when the frequency converter (1) is in the stand-by mode, in order to reduce the dissipation power consumed, the charging circuit (34, 44) is configured: i) to decrease the float voltage (U_L supplied to the direct-current intermediate circuit (13) when the switch (2, 3, 4) is open for shifting the frequency converter (1) from the stand-by mode to the energy-saving mode, and ii) to increase the float voltage (U_L) supplied to the direct-current intermediate circuit (13) when the switch (2, 3, 4) is open for restoring the frequency converter (1) from the energy-saving mode to the stand-by mode before the switch (2, 3, 4) is closed. The application also contains independent claims for a method and elevator.

Description

Frequency converter with intermediate circuit and method for the reduction of power consumption of intermediate circuit of

frequency converter that is in stand-by mode, and elevator

Field of invention

The invention relates to the field of electrical engineering and especially to frequency converters with an intermediate circuit. The invention also relates to the field of elevator technology.

Technical background

In order to reduce the operating costs, the objective is that an elevator saves energy, in other words consumes little energy. As the energy efficiency requirements are becoming increasingly stringent, a reduction in power consumption by a few dozen Watts or even just a few Watts may have great significance not only in the energy efficiency classification of an elevator but also in the energy efficiency of an elevator.

Elevators consuming little energy can be classified in the best A energy efficiency class in an assessment based on standard VDI 4707 ("Energy efficiency labels for elevators").

Most of the motor controls in elevator drives are currently carried out using constant voltage intermediate circuit technology in the manner described in the introductory part of the

applicant's European patent EP 1 444 770 Bl. This includes a motor bridge and a network bridge with insulated-gate bipolar

transistors (IGBT) . A capacitor bank that equalises the wave form of the voltage is needed between the bridges. The capacitor bank is usually made of two series-connected capacitors. A necessary number of these series-connected capacitor banks are usually connected in parallel, depending on the size of the elevator drive. The charging of the intermediate circuit is carried out by means of a separate charging resistance connection. A prior art charging resistance connection maintains a full voltage in the capacitors also during stand-by mode, in other words when the elevator is waiting for an elevator call at a floor level. In this case, the network bridge of the frequency converter is open. Objective of invention

Keeping the intermediate circuit charged increases the dissipation power of motor control carried out with a frequency converter considerably when the frequency converter is in the stand-by mode, in other words when the network bridge is open, in other words when the switch of the frequency converter between the contacts on the side of the electric network and the rectifier is open.

On the other hand, the intermediate circuit needs to be charged before closing the switch between the contacts on the side of the electric network and the rectifier so that the capacitors would not be broken. Otherwise, the charging current caused by the voltage connected over uncharged capacitors might break the capacitors . The objective according to a first aspect of the invention is to enable a reduction in the dissipation power of motor control carried out with a frequency converter when the frequency

converter is in the stand-by mode.

This objective can be accomplished by means of the frequency converter with an intermediate circuit according to the

independent claim 1 and by means of the method for the reduction of the power consumption of the intermediate circuit of a

frequency converter that is in the stand-by mode according to the parallel independent 8. It is also very important to keep the intermediate circuit charged if electric power is taken from the charging circuit for the power supply of the control electronics of the frequency converter when the switch between the contacts on the side of the electric network and the rectifier is open. This may be necessary for example because in this way the control electronics of the frequency converter can be kept in readiness for use, in other words in a state where the frequency converter can be brought to operation quickly whenever necessary. The objective according to a second aspect of the invention is to also enable a reduction in the dissipation power of a frequency converter where electric power is taken from the intermediate circuit of the frequency converter for the power supply of the control electronics of the frequency, converter when the switch between the contacts on the side of the electric network and the rectifier is open. This objective can be accomplished by means of the frequency converter according to the dependent claim 2 and by means of the method according to the dependent method claim 9 when the frequency converter used in the method is a frequency

converter according to claim 2.

The objective according to a third aspect of the invention is to enable the implementation of an elevator with a better energy efficiency than before. This objective can be accomplished by means of an elevator according to the parallel independent claim.

The dependent claims describe the preferred embodiments of the frequency converter and method.

Advantages of invention

A frequency converter with an intermediate circuit for driving a motor comprises a rectifier connected to the contacts on the side of the electric network by means of a switch, an inverter

connected to the contacts on the side of the motor, and a direct- current intermediate circuit between the rectifier and the inverter, which direct-current intermediate circuit comprises at least one capacitor bank comprising a balancing resistor for equalising the voltage over the direct-current intermediate circuit in the operating situation of the motor.

Moreover, the frequency converter comprises a charging circuit which is connected or connectable to the direct-current

intermediate circuit for supplying a float voltage to the direct- current intermediate circuit when the switch is open in order to keep the frequency converter in the stand-by mode.

The charging circuit is configured: i) to decrease the float voltage supplied to the direct-current intermediate circuit when the switch is open for shifting the frequency converter from the stand-by mode to the energy-saving mode, and ii) to increase the float voltage supplied to the direct-current intermediate circuit when the switch is open for restoring the frequency converter from the energy- saving mode to the stand-by mode before the switch is closed.

The float voltage in the energy-saving mode, produced by a charging circuity according to the invention, is lower than the float voltage in the stand-by mode. The invention stems from the inventive idea that in a prior art frequency converter the dissipation power in the stand-by mode is mostly generated in the balancing resistors of the capacitor banks. When the magnitude of the current travelling through the balancing resistors is reduced by decreasing the voltage over the balancing resistors, the power consumption of the balancing resistors can be reduced. This enables a reduction in the dissipation power of the entire frequency converter-.

A frequency converter according to a second aspect of the

invention also comprises power supply of the control electronics of the frequency converter, where the power supply is connected or connectable to the direct-current intermediate circuit, or comprises the connections for this purpose. The power supply of the control electronics also comprises a DC/DC converter, which is adapted to take electric power from the direct-current

intermediate circuit both when the frequency converter is in the stand-by mode and when the frequency converter is in the energy- saving mode, and to give electric power to the control electronics using essentially the same voltage both when the frequency converter is in the stand-by mode and when the frequency converter is in the energy-saving mode. In this way, the structure of the frequency converter can be kept more simple, because electric power can be taken from the charging circuit for the power supply of the control electronics both in the stand-by mode and in the energy- saving mode. According to a preferred aspect, the voltage of the direct-current intermediate circuit in the energy-saving mode is approx. 50 Vdc (most preferably 50 Vdc + 5 Vdc) , and in the stand-by mode approximately 500 Vdc (most preferably 500 Vdc ± 50 Vdc) . In this way, the dissipation power in the energy-saving mode can be decreased down to one hundredth of the dissipation power in the stand-by mode, with the control electronics of the frequency converter still being ready for operation.

The charging circuit can comprise a stand-by connection, where a step-down resistance can be bypassed by means of a stand-by switch. When the step-down resistance is connected, the charging circuit produces a lower voltage for the energy-saving mode, and when the step-down resistance is bypassed, the charging circuit produces a higher voltage for the stand-by mode. In this case, the frequency converter can be configured to shift between the energy- saving mode and the stand-by mode by adjusting the impedance and/or by over-connecting the step-down resistance or by removing the bypassing on the basis of a command (CMD) given by the elevator control. The method presented here enables the

implementation of the frequency converter by using relatively simple components.

In addition to the stand-by connection or as an alternative to it, the charging circuit can comprise a controllable active connection and/or switched-mode power supply, which is controllable to produce a lower voltage for the energy- saving mode and a higher voltage for the stand-by mode. In this case, the frequency converter can be configured to adjust the voltage produced by the active connection and/or switched-mode power supply between the energy- saving mode and the stand-by mode on the basis of a command given by the elevator control. The method presented here enables the implementation of the frequency converter at a relatively good efficiency of the charging circuit.

In the method for the reduction of the power consumption of the intermediate circuit of a frequency converter that is in the stand-by mode i) the float voltage supplied to the direct-current intermediate circuit when the switch between the contacts on the side of the electric network and the rectifier is open is

decreased in order to shift the frequency converter from the stand-by mode to the energy-saving mode, and ii) the float voltage supplied to the direct-current intermediate circuit when the switch is open is increased in order to restore the frequency converter from the energy-saving mode to the stand-by mode before the switch is closed.

The method is preferably implemented by means of a frequency converter according to the first or second aspect of the

invention.

The float voltage can be changed in order to shift the frequency converter between the energy- saving mode and the stand-by mode on the basis of a command given by the elevator control. This facilitates the implementation of an energy-saving frequency converter to be controlled by the elevator control.

According to a preferred aspect, the lower and the higher float voltage can be selected by controlling a switch, resistance, adjustable impedance, controllable active connection and/or switched-mode power supply in the charging circuit.

An elevator according to a third aspect of the invention includes a frequency converter according to a first or second aspect of the invention, and/or a method according to a first or second aspect of the invention is used in the elevator to reduce the dissipation power consumed in the stand-by mode.

List of drawings

In what follows, we present the operating principle of the frequency converters and methods according to the invention in more detail by going through the exemplary embodiments in the enclosed drawings. Of the drawings:

FIG 1 shows a frequency converter with an intermediate circuit;

FIG 2 shows a charging circuit used in a prior art frequency

converter with an intermediate circuit;

FIG 3 shows a charging circuit including a stand-by connection of a frequency converter according to the invention, which charging circuit produces, when the step-down resistance is connected, a lower float voltage for the energy-saving mode, and when the step-down resistance is bypassed, the charging circuit produces a higher float voltage for the stand-by mode; and

FIG 4 shows a second charging circuit including a switched-mode power supply of a frequency converter according to the invention, which charging circuit is controllable to produce a lower float voltage for the energy- saving mode and a higher float voltage for the stand-by mode.

The same reference numbers refer to the same technical parts in all FIG. Detailed description

FIG 1 shows a frequency converter 1 that includes an intermediate circuit 13, for driving a motor M. The frequency converter 1 comprises a rectifier 11 connected to the contacts R, S, T (for example corresponding to phases LI, L2 , L3) on the side of the electric network via a switch 2, 3, 4. The switch 2, 3, 4 can be implemented for example as a contactor or as an IGBT switch.

Moreover, the frequency converter 1 comprises an inverter 12 connected to the contacts U, V, W on the side of the motor M, and a direct-current intermediate circuit 13 between the rectifier 11 and inverter 12, which direct-current intermediate circuit 13 comprises for example two capacitor banks 18, 19 (most preferably electrolytic capacitor banks) and their balancing resistors 16, 17. The number of the balancing resistors 16, 17 and the number of the capacitors 18, 19 can be other, for example 1, 2, 3 or . They can be connected in a manner other than that shown in FIG 1, because the purpose of the connection is to aim to equalise the voltage U_c over the direct-current intermediate circuit 13 in the operating situation of the motor M.

The capacitors used in the capacitor banks 18, 19 are most preferably electrolytic capacitors, aluminium capacitors or plastic capacitors. Electrolytic capacitors are commonly used because of their high capacitance. Moreover, the frequency converter 1 comprises a charging circuit 34, 44 which is connected or connectable to the direct-current intermediate circuit 13 for supplying a float voltage U_L to the direct-current intermediate circuit 13 when the switch 2, 3, 4 is open in order to keep the frequency converter 1 in the stand-by mode.

The charging circuit 34, 44 is configured i) to decrease the float voltage U_L supplied to the direct-current intermediate circuit 13 when the switch 2, 3, 4 is open in order to shift the frequency converter 1 from the stand-by mode to the energy-saving mode, and ii) to increase the float voltage U_L supplied to the direct- current intermediate circuit 13 when the switch 2, 3, 4 is open in order to restore the frequency converter 1 from the energy-saving mode to the stand-by mode before the switch 2, 3, 4 is closed.

The float voltage U_L of the direct-current intermediate circuit 13 in the energy-saving mode can be approx. 50 Vdc, most preferably 50 Vdc + 5 Vdc, and in the stand-by mode approximately 500 Vdc, most preferably 500 Vdc + 50 Vdc. The float voltages U_L can be chosen to be other, depending on how much the dissipation power of a frequency converter that is in the stand-by mode needs to be reduced.

In order to understand the operation of the charging circuits 34, 44, it is first necessary to study the structure of a charging circuit 14 of a prior art frequency converter shown in FIG 2. The charging circuit 14 is connected for example between phases LI, L2 by the contacts R, S on the side of the electric network. The difference in potential (for example 400 Vac) coming from between the contacts R, S is reduced (and the current is limited at the same time) by means of balancing resistors. 21, 22, after which the voltage is rectified in the rectifier 23. The float voltage U_L coming from the rectifier 23 is connected over the direct-current intermediate circuit 13.

If a float voltage U_L of approximately 500 Vdc is maintained in the direct-current intermediate circuit 13, the dissipation power of the balancing resistors 16, 17 of the capacitor banks 18, 19 is in this case P_DISS = (500 V)² / R, where R = combined resistance of the balancing resistors 16, 17.

The capacitor banks 18, 19 have a relatively high internal leakage current, up to several milliamperes . In order to ensure that the maximum voltage of an individual capacitor bank 18, 19 is not exceeded, so-called balancing resistors 16, 17 must be connected over the capacitor banks 18, 19. The current travelling through the balancing resistors 16, 17 is considerably (5 to 10 times) higher than the leakage current. The balancing resistors 16, 18 must also be dimensioned to have a sufficiently low Ohm value in order to ensure that the capacitor banks 18, 19 are discharged within the prescribed period of time so that the frequency converter 1 would not be dangerous in a maintenance situation. When the frequency converter 1 is in the stand-by mode, the direct-current intermediate circuit 13 cannot usually be

discharged, especially if the power required by the control electronics 15 of the frequency converter 1 has been generated by low-voltage power connected to the intermediate circuit (power supply 15' of control electronics 15) . It is advantageous if the supply voltage can be maintained by means of the control

electronics 15 so that sufficiently quick response can be ensured when the elevator is called the next time, whereby the motor M is operated by means of the frequency converter 1. This causes such a great power consumption when the frequency converter 1 is in the stand-by mode that it is practically impossible to reach the best A-class in accordance with standard VDI 4707 except only when each frequency converter 1 is in almost full-capacity operation. FIG 3 shows the charging circuit 34. The charging circuit 34 comprises a stand-by connection 30, where a step-down resistance 38 can be bypassed by means of a stand-by switch 39. When the step-down resistance 38 is connected, the charging circuit 34 produces a lower float voltage U_L for the energy- saving mode, and when the step-down resistance 38 is bypassed, the charging circuit 34 produces a higher float voltage U_L for the stand-by mode.

The frequency converter 1 can be configured to shift between the energy- saving mode and the stand-by mode by bypassing the step- down resistance 38 or by removing the bypassing on the basis of a command CMD given by the elevator control.

When the float voltage U_L connected from the charging circuit 34, 44 of the direct-current intermediate circuit 13 when shifting from the stand-by mode to the energy- saving mode is dropped for example to 50 volts (which is sufficient for the power supply 15' of the control electronics 15) , the corresponding dissipation power of the balancing resistors is P_Diss _STB = (50 V)² / R.

The ratio of the dissipation powers P_Di_{SS STB} / P_DISS is approximately 0.01%, in other words the dissipation power of the balancing resistors can be reduced to one hundredth of the original. The charging circuit 44 according to the invention can be

implemented even more preferably than this by utilising switched- mode power supply technology. The advantages of switched-mode power supply include an opportunity to stabilise the voltage of the intermediate circuit 13, whereupon the load has no impact on voltage variation. Moreover, by means of the power transfer 49 of the switched-mode power supply the supply voltage and the

intermediate circuit 13 can be separated from each other

galvanically . FIG 4 shows the charging circuit 44. The charging circuit 44 comprises switched-mode power supply 48, which is connected to the rectifier 23 via power transfer 49. The switched-mode power supply 48 is controllable to produce a lower voltage for the energy- saving mode and a higher voltage for the stand-by mode.

The frequency converter 1 can be configured to adjust the voltage produced by the switched-mode power supply 48 between the energy- saving mode and the stand-by mode on the basis of a command CMD given by the elevator control.

According to a second aspect of the invention, the frequency converter 1 can comprise a power supply 15' of the control electronics 15 of the frequency converter 1, where the power supply 15' is connected or connectable to the direct-current intermediate circuit 13, or comprises the connections Tl, T2 for this purpose. In this case, the power supply 15' of the control electronics 15 can comprise a DC/DC converter, which is adapted to take electric power from the direct-current intermediate circuit 13 both when the frequency converter 1 is in the stand-by mode and when the frequency converter 1 is in the energy-saving mode, and to give electric power to the control electronics 15 using essentially the same voltage (for example 25 Vdc, but can be other, for example 12 Vdc) both when the frequency converter 1 is in the stand-by mode and when the frequency converter 1 is in the energy- saving mode.

In other words, the dissipation powers during the standstill of the elevator can be reduced by means of the charging circuits 34, 44 of the capacitors of the direct-current intermediate circuit 13 of a frequency converter 1 of an elevator. The idea is to either increase the impedance of the charging circuit 34 during the standstill of the elevator so that the intermediate circuit voltage drops to approximately 50 volts, which is needed to keep the control electronics of the elevator operational, or to implement the charging circuit 44 by means of a controllable active connection, with which the float voltage U_L can be set by switching power semiconductors.

The invention should not be understood to be limited only by the below claims, but the invention is to be understood to include all their legal equivalents and the combinations of the embodiments presented.

List of reference numbers used:

LI, L2 , L3 phases

R, S, T contacts on the side of the electric network

U, V, W contacts on the motor side

Tl, T2 connections for the control electronics of the

frequency converter

M motor

U_c voltage over the charging circuit in the operating situation of the motor

U_L float voltage

CMD command

I frequency converter

2, 3, 4 switch (for example insulated-gate bipolar transistors)

II rectifier

12 inverter

13 direct-current intermediate circuit

15 control electronics of the frequency converter

15' power supply of the control electronics of the

frequency converter (preferably a DC/DC converter)

16, 17 balancing resistor

18, 19 capacitor bank

21, 22 balancing resistor

23 rectifier

25 30 stand-by connection

34 charging circuit

38 step-down resistance

39 stand-by switch

44 charging circuit

30 48 switched-mode power supply

49 power transfer

Claims

Claims :

1. A frequency converter (1) with an intermediate circuit (13) for driving a motor (M) , characterized in that:

The frequency converter (1) comprises: - a rectifier (11) connected to the contacts (R, S, T) on the side of the electric network via a switch (2, 3, 4) ;

- an inverter (12) connected to the contacts (U, V, W) on the side of the motor (M) ; - a direct-current intermediate circuit (13) between the rectifier (11) and the inverter (12) , which direct- current intermediate circuit (13) comprises at least one capacitor bank (18, 19) comprising a balancing resistor (16, 17) for equalising the voltage (U_c) over the direct-current intermediate circuit (13) in the

, operating situation of the motor (M) ;

- a charging circuit (34, 44) which is connected or connectable to the direct-current intermediate circuit (13) for supplying a float voltage (Uj to the direct- current intermediate circuit (13) when the switch (2,

3, 4) is open in order to keep the frequency converter (1) in the stand-by mode; and where the charging circuit (34, 44) is configured: i) to decrease the float voltage (U_L) supplied to the direct -current intermediate circuit (13) when the switch (2, 3, 4) is open for shifting the frequency converter (1) from the stand-by mode to the energy- saving mode, and ii) to increase the float voltage (U_L) supplied to the direct-current intermediate circuit (13) when the switch (2, 3, 4) is open for restoring the frequency converter (1) from the energy- saving mode to the standby mode before the switch (2, 3, 4) is closed.

2. A frequency converter (1) according to claim 1, where the frequency converter (1) comprises power supply (15') of the control electronics (15) of the frequency converter (1), where the power supply (15') is connected or connectable to the direct- current intermediate circuit (13), or comprises the connections (Tl, T2) for this purpose, and where the power supply (15') of the control electronics (15) comprises a DC/DC converter, which is adapted to take electric power from the direct-current

intermediate circuit (13) both when the frequency converter (1) is in the stand-by mode and when the frequency converter (1) is in the energy-saving mode, and to give electric power to the control electronics (15) using essentially the same voltage both when the frequency converter (1) is in the stand-by mode and when the frequency converter (1) is in the energy- saving mode.

3. A frequency converter (1) according to claim 1 or 2 , where the float voltage (U_L) of the direct-current intermediate circuit (13) in the energy-saving mode is approx. 50 Vdc, most preferably 50 Vdc + 5 Vdc, and in the stand-by mode approximately 500 Vdc, most preferably 500 Vdc + 50 Vdc.

4. A frequency converter (1) according to any one of the preceding claims, where the charging circuit (34) comprises a stand-by connection (30) , where a step-down resistance (38) can be bypassed by means of a stand-by switch (39) . When the step-down resistance (38) is connected, the charging circuit (34) produces a lower float voltage (U_L) for the energy-saving mode, and when the step- down resistance (38) is bypassed, the charging circuit (34) produces a higher float voltage (U_L) for the stand-by mode.

5. A frequency converter (1) according to claim 4, where the frequency converter (1) is configured to shift between the energy- saving mode and the stand-by mode by adjusting the impedance and/or by bypassing the step-down resistance (38) or by removing the bypassing on the basis of a command (CMD) given by the elevator control .

6. A frequency converter (1) according to any one of the preceding claims, where the charging circuit (44) comprises a controllable active connection and/or switched-mode power supply (48), which is controllable to produce a lower voltage for the energy- saving mode and a higher voltage for the stand-by mode.

7. A frequency converter (1) according to claim 6, where the frequency converter (1) is configured to adjust the voltage produced by the active connection and/or switched-mode power supply (48) between the energy- saving mode and the stand-by mode on the basis of a command (CMD) given by the elevator control.

8. A method for the reduction of power consumption of an

intermediate circuit (13) of a frequency converter (1) that is in the stand-by mode, characterized in that: i) the float voltage

(U_L) supplied to the direct-current intermediate circuit (13) when the switch (2, 3, 4) between the contacts (R, S, T) on the side of the electric network and the rectifier (11) is open is decreased for shifting the frequency converter (1) from the stand-by mode to the energy-saving mode, and ii) the float voltage (U_L) supplied to the direct-current intermediate circuit (13) when the switch (2, 3, 4) is open is increased for restoring the frequency converter (1) from the energy- saving mode to the stand-by mode before the switch (2, 3, 4) is closed.

9. A method according to claim 8, where the method is implemented by means of a frequency converter (1) according to any one of the claims 1 to 7.

10. A method according to claim 8 or 9, where the float voltage (U_L) is changed in order to shift the frequency converter (1) between the energy-saving mode and the stand-by mode on the basis of a command (CMD) given by the elevator control.

11. A method according to any one of the claims 8 to 10, where the lower and higher float voltage are selected by controlling a switch (39) , adjustable impedance, resistance (38) , controllable active connection and/or switched-mode power supply (48) in the charging circuit (34, 44) .

12. An elevator which includes a frequency converter according to any one of the claims 1 to 7 and/or where a method according to any one of the claims 8 to 11 is used in order to decrease the dissipation power consumed in the stand-by mode.