GB2484512A

GB2484512A - Power supply based on clock signals

Info

Publication number: GB2484512A
Application number: GB1017312.8A
Authority: GB
Inventors: Simon Wilton
Original assignee: Honeywell Technologies SARL
Current assignee: Garrett Motion SARL
Priority date: 2010-10-13
Filing date: 2010-10-13
Publication date: 2012-04-18
Anticipated expiration: 2030-10-13
Also published as: FR2966302A1; FR2966302B1; GB201017312D0; GB2484512B

Abstract

A control system provides control signals for at least one AC motor having a clock generator 15 to generate first and second clock signals that alternate between an on and off state, the first clock signal being in the off state when the second clock signal is in the on state. A supply generator 11 receives the clock signals, and generates a power supply for the AC motor when the control signal indicates that the AC motor is to be operated. The power supply generated by the supply generator 11 is at a first voltage level when the first clock signal is in the on state, at a second voltage level when the first clock signal is in the off state and the second clock signal is in the on state, and at an intermediate voltage level between the first and second voltage levels when the first and second clock signals are in the off state.

Description

Control systems and methods

Background of the Invent ion

The present invention concerns control systems. The invention is particularly, although not exclusively, applicable to Building Management Systems (BMS5), that is, systems for managing the devices that control the environment within a building. More particularly, although not exclusively, the invention relates to the control of actuators in a BMS.

It is common for AC motors to be used in a BMS, as actuators to control the position of valves, dampers and other small items of the BMS. AC motors that take a 24V 50/60Hz AC supply are frequently used.

Historically, commercial buildings such as office buildings have included a transformer to provide a 24V 50/60Hz AC supply, which is used to operate various devices such as power, exhaust, heating and cooling systems within the building. This supply can be used by a BMS to operate the AC motors, by controlling the supply of the AC to the motors by means of low-cost triac switches.

However, in newer designs of building such a transformer is no longer required, and consequently no 24V 50/60Hz AC supply is available for use by the BMS. One solution is to provide a transformer specifically for use by the BMS to operate the motors. However, this is costly in terms of additional parts being required, and inefficient in terms of energy usage.

The present invention seeks to mitigate the above-mentioned problems.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a control system comprising: a management system arranged to provide at least one control signal for at least one AC motor; a clock generator arranged to generate first and second clock signals that alternate between an off state and an on state, the first clock signal being in the off state when the second clock signal is in the on state; a supply generator arranged to receive the first and second clock signals from the clock generator, and further arranged to generate a power supply for the AC motor when the control signal from the management system indicates that the AC motor is to be operated; wherein the power supply generated by the supply generator is at a first voltage level when the first clock signal is in the on state; wherein the power supply generated by the supply generator is at a second voltage level when the first clock signal is in the off state and the second clock signal is in the on state;

S

and wherein the power supply generated by the supply generator is at a intermediate voltage level between the first and second voltage levels when the first and second clock signals are in the off state.

The management system controls the internal environment of the building, by providing control signals f or the AC motors that may for example act as actuators in a BMS. A clock generator generates first and second clock signals, which are used by the supply generator to create a power supply for the AC motor when the control system indicates that the motor should be operated. The first and second clock signals alternate between on and off states (high and low states, for example) . When the first clock signal is in the on state, the power supply is provided at the first voltage level (for example a positive voltage level) . If, on the other hand, the second clock signal is in the on state, and so the first clock signal is necessarily in the off state, the power supply is provided at the second voltage level (for example a negative voltage level) Finally, if both the first and second clock signals are in the off state, the power supply is provided at the intermediate voltage level (for example electrical ground) In this way, the supply generator is able to use the first and second clock signals to provide a power supply that moves between negative, ground and positive voltage levels. This very roughly approximates a sinusoidal AC supply, and in particular is able to provide output torque from the AC motor, and heating within the AC motor, similar to that generated by an AC supply. Thus, a power supply can be provided to operate the AC motor, without an AC transformer that directly provides an AC supply being required.

Preferably, the AC motor is intended to take a 24V 50/60HZ AC supply. In this case, the first voltage level may be ÷28'!, the second voltage level -28V, *and the intermediate voltage level 0V. The AC motor may be a unidirectional motor or a bidirectional motor, for example.

In this case that the motor is bidirectional, first and second supplies of power may be generated based on first and second control signals from the management system, or from a single control signal with multiple states, for example.

Preferably, the second clock signal is in the off state when the first clock signal is in the on state. More preferably, the first and second clock signals are offset by half a period.

Preferably, the first clock signal is in the on state for a shorter period than it is in the off state. Further preferably, the second clock signal is in the on state for a shorter period than it is in the off state. This allows the first and second clock signals to be simultaneously in the off state before and after either of them being in the on state. Preferably, the first and second clock signals are in the off state for 55-65% of a period. More preferably, the first and second clock signals are in the off state for 60% of a period.

Advantageously, the management system is arranged to provide a plurality of control signals each associated with a respective AC motor. Preferably, the system comprises a plurality of supply generators each associated with a respective AC motor. This allows a plurality of AC motors to be controlled by the management system.

Preferably, the system further comprises a signal generator arranged to receive the control signal or signals S from the management system and the first and second clock signals from the clock generator, and further arranged to transmit the first and second clock signals to a supply generator when the control signal from the management system associated with the respective AC motor indicates that the motor is to be operated. In particular, this allows a single clock generator to be used in the control of a plurality of motors.

Advantageously, the control system is a system for controlling the internal environment of a building. This is a field for which the invention is particularly applicable.

In accordance with a second aspect of the invention there is provided a method of operating a control system comprising a management system arranged to provide at least one control signal for at least one AC motor, the method comprising the steps of: generating first and second clock signals that alternate between an off state and an on state, the first clock signal being in the off state when the second clock signal is in the on state; generating a power supply for the AC motor based upon the first and second clock signals when the control signal from the management system indicates that the AC motor is to be operated; wherein the power supply is at a first voltage level when the first clock signal is in the on state; wherein the power supply is at a second voltage level when the first clock signal is in the off state and the second clock signal is in the on state; and wherein the power supply is at a intermediate voltage level between the first and second voltage levels when the first and second clock signals are in the off state.

Preferably, the second clock signal is in the off state when the first clock signal is in the on state. Preferably, the first clock signal is in the on state for a shorter period than it is in the off state. Advantageously, the management system is arranged to provide a plurality of control signals each associated with a respective AC motor.

Advantageously, the method further comprises the steps of generating a power supply for each AC motor based upon the first and second clock signals when the associated control signal indicates that the AC motor is to be operated.

Advantageously, the control system is for controlling the internal environment of a building.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention are now described by way of example only with reference to the accompanying figures of which: Figure 1 is a diagram of a BMS in accordance with a first embodiment of the invention; Figure 2 is a diagram of a BMS in accordance with a second embodiment of the invention; Figure 3a is a graph of a first clock signal provided by the clock generator of Figures 1 or 2; Figure 3b is a graph of a second clock signal provided by the signal generator of Figure 1 or 2; Figure 4 is a circuit diagram of the signal generator of Figures 1 or 2; Figure 5 is a circuit diagram of the supply generator of Figures 1 or 2; Figure 6 is a graph of the output of the supply generator of Figure 3.

Detailed Description

A EMS in accordance with a first embodiment of the invention is shown in Figure 1. The EMS 1 comprises a management system 10. The management system 10 receives data on conditions within the building (for example the temperature in different areas within the building), and controls devices within the building (for example air conditioning units), in order to control the environment within the building based upon parameters set by a user.

The B['4S 1 further comprises a signal generator 11, which receives control signals from the management system 10. The signal generator 11 also receives clock signals from a clock generator 15. The signal generator 11 in turn generates drive signals and sends them to supply generators 12a, 12b, l2c, 12d. The supply generators 12a, 12b, l2c, 12d then supply power to AC motors 13a, 13b, l3c and l3d respectively. The AC motors l3a, 13b, l3c and l3d are unidirectional motors which are intended to take a 24V 50/60Hz AC supply; each of the motors (and indeed the other elements of the BMS 1) is also connected to electrical ground (not shown) In the embodiment of Figure 1, the management system 10 provides control signals to control operation of each of the AC motors 13a, l3b, l3c and 13d respectively. The control signals provided by the management system 10 are logic signals, having low and high states of 011 and 3.3V respectively. Of course, the skilled person would appreciate that alternative logic schemes that use different high and low logic levels would be equally applicable to the invention.

In addition, the clock generator 15 provides first and second clock signals, which are again logic signals having low and high states of OV and 3.311 respectively.

The four control signals from the management system 10 are expanded by the signal generator 11, using the first and second clock signals provided by the clock generator 15, into four pairs of drive signals, as described in more detail below. The drive signals are again logic signals having low and high states of OV and 3.3V respectively.

Each of the supply generators 12a, l2b, l2c and 12d receives one of the paiiEs of drive signals from the signal generator 11, and uses it to create a power supply with a low level of -28V and a high level of 28V, again as described in more detail below. This power supply is provided to the supply generator's respective AC motor 13a, l3b, 13c or 13d. Thus, the management system 10 is able to control the AC motors 13a, l3b, 13c and 13d by means of the signal generator 11 and supply generators 12a, 12b, 12c and l2d.

A EMS in accordance with a second embodiment of the invention is shown in Figure 1. Similarly to the EMS 1 of Figure 1, the EMS 2 of Figure 2 comprises a management system 10, a clock generator 15, a signal generator 11 which receives signals from the management system 10 and the clock generator 15, and supply generators 12a, 12b, 12c, l2d.

However, rather than the four unidirectional AC motors 13a, 13b, 13c, l3d, the EMS 2 of Figure 2 comprises two bidirectional AC motors 14a and 14b. Each of the AC motors 14a and 14b is intended to take a 24V 50/60Hz AC supply, and is also connected to electrical ground (not shown).

However, as the AC motors 14a and l4b are bidirectional, each can take two supplies of power, to operate them in either direction. Consequently, AC motor l4a receives a supply of power from supply generators 12a and 12b, and AC motor 14b receives a supply of power from supply generators 12c and l2d. Thus, similarly to the EMS 1 of Figure 1, the -10 -management system 10 of the EMS 2 of Figure 2 is able to control the AC motors 14a and 14b by means of the signal generator 11 and supply generators 12a, 12b, 12c and l2d.

S The operation of the embodiment of Figure 1 is now described in more detail. The embodiment of Figure 2 operates similarly, except that power is supplied to the two bidirectional AC motors l4a and 14b rather than the four unidirectional AC motors 13a, l3b, 13c and 13d.

As discussed above, the clock generator 15 provides first and second clock signals to the signal generator 11.

The first and second clock signals are shown in Figures 3a and 3b respectively. (While the clock signals are logic signals having a low state of OV, for clarity the x-axes of Figures 3a and 3b are positioned below OV.) Each clock signal has a frequency of 50Hz and duty cycle of 40%; in other words, the signals alternate being high for a period of l2ms, and low for a period of Bms. The first and second singles are offset by a period of lOms. Thus, as can be seen, each clock signal is in a high state while the other is in a low state, with both clock signals being in a low state simultaneously for a period of 2ms either side of the high state.

The signal generator 11 is shown in more detail in Figure 3. The signal generator 11 comprises a complex programmable logic device (CPLD) 20. The signal generator 11 uses the first and second clock signals from the clock generator 15 (P34 and PBS in Figure 3) to expand the four control signals (P30 to P33) from the management system 10 into four pairs of drive signals (Chop 11 and Chop_hl to -11 -Chop_l4 and Chop_h4). Control signal PBO is expanded into drive signals Chop_li and Chop_hi as follows: PBO Chop_li Chop hi Low Low ---Low High PB4 PBS In other words, when control signal P30 is low, both supply signals Chop 11 and Chophl are low. When control signal P30 is high, drive signal Chop_li provides the first clock signal from PB4, while drive signal Chop_hi provides the second clock signal from P35.

The other pairs of drive signals are generated from the first and second clock signals in a similar way, similarly, as follows: P01 Cbop_12 Chop_h2 Low --Low Low High P34 PBS -P02 -Chop 13 Chop_h3 Low Low -Low High P34 PBS P03 Chop_14 Chop_h4 Low Low --Low High P34 PBS The supply generator l2a is shown in more detail in Figure 5. Supply generators l2b, l2c and l2d are identical -12 -in construction. The supply generator l2a comprises in particular complimentary (NIP) MOSFET transistors 37 and 38.

The supply generator l2a receives the pair of drive signals Chop_li and Chop_hl (31 and 32 in Figure 5) from the signal generator 11. The supply generator l2a is also connected to a -28V DC supply 34 and a +28V DC supply 35. The supply generator 12a outputs a power supply 36 to the AC motor 13a.

The gate of the transistor 37 is connected (via some other components) to the drive signal Chop_li 31 from the signal generator 11. The drain of transistor 37 is connected to the -28V DC supply 34. The source of transistor 37 is connected (via some other components) to the power supply 36.

The gate of the transistor 38 is connected (via some other components) to the drive signal Chop_hi 32 from the signal generator 11. The drain of transistor 38 is connected (via some other components) to the power supply 36. The source of transistor 38 is connected to the ÷28V DC supply 35.

The supply generator 12a operates as follows.

If both drive signals Chop_ll 31 and Chop_hi 32 are low, transistors 37 and 38 are closed, and no power is output via the power supply 36.

If drive signal Chop_li 31 is high, transistor 37 opens, pulling the power supply 36 down to the -28V DC supply 34. If on the other hand Chop_hi 32 is high, transistor 38 opens, pulling the power supply 36 up to the ÷28V DC supply 35. (Due to the nature of the first and second clock signals P84 and P35, and the logic of the -13 -signal generator 11, it is not possible for drive signals Chop_ll 31 and Chop_hi 32 to be high simultaneously.) Thus, when control signal PBO is low, drive signais Chop_ll 31 and Chop_hi 32 will be low, and no power will be output via the power supply 36. In contrast, when control signal PBO is high, drive signals Chop_li 31 and Chop_hl 32 will provide the first and second clock signals PB4 and PBS respectively. The power supply 36 when generated by the combination of the first and second ciock signals PB4 and PBS by the supply generator l2a is shown in Figure 6. (For clarity, the x-axis of Figure 6 is positioned below -28V.) As can be seen, the power supply 36 repeats the sequence of -28V for 8ms (when first clock signal PB4 is high and second clock signal PBS is low), OV for 2ms (when both clock signals PB4 and PBS are low), +28V for 8ms (when first clock signal PB4 is low and second clock signal PBS is high), and OV for 2ms (when both clock signals PB4 and PBS are low).

While the power supply 36 does not precisely mirror a sinusoidal 24V AC supply, it is sufficiently similar to power the AC motor l3a, providing output torque from the AC motor l3a, and heating within the AC motor 13a, similar to that generated by a 24V AC sinusoidal power supply.

It can thus be seen that the clock generator 15, signal generator 11 and supply generators l2a, 12b, l2c and l2d in combination act on control signals from the management system 10 to provide power supplies to operate the AC motors l3a, 13b, 13c and l3d, without requiring an AC transformer that directly provides a 24V AC supply.

-14 -Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the. art that the invention lends itself to many different variations not specifically illustrated herein.

For example, the skilled person will appreciate that the invention equally applies to embodiments that provide power supplies for greater numbers of motors. Further, the invention applies to embodiments comprising a combination of unidirectional and bidirectional motors. The skilled person will also appreciate that alternative forms of circuit could be used. For example, N/N MOSFET, P/P MOSFET, IGBT and/or bipolar transistors, or any other class D output stage, could be used in place of the described N/P MOSFET transistors. Similarly, variations of an H' bridge circuit could be used. As another example, the signal generator 11 and clock generator 15 could be implemented entirely using firmware.

Claims

-15 -Claims 1. A control system comprising: a management system arranged to provide at least one control signal for at least one AC motor; a clock generator arranged to generate first and second clock signals that alternate between an off state and an on state, the first clock signal being in the off state when the second clock signal is in the on state; a supply generator arranged to receive the first and second clock signals from the clock generator, and further arranged to generate a power supply for the AC motor when the control signal from the management system indicates that the AC motor is to be operated; wherein the power supply generated by the supply generator is at a first voltage level when the first clock signal is in the on state; wherein the power supply generated by the supply generator is at a second voltage level when the first clock signal is in the off state and the second clock signal is in the on state; and wherein the power supply generated by the supply generator is at a intermediate voltage level between the first and second voltage levels when the first and second clock signals are in the off state.
2. A system as claimed in claim 1, wherein the second clock signal is in the of f state when the first clock signal is in the on state.

-16 -
3. A system as claimed in claim 1 or 2, wherein the first clock signal is in the on state for a shorter period than it is in the off state.
4. A system as claimed in any preceding claim, wherein the management system is arranged to provide a plurality of control signals each associated with a respective AC motor.
5. A system as claimed in claim 4, comprising a plurality of supply generators each associated with a respective AC motor.
6. A system as claimed in any preceding claim, further comprising a signal generator arranged to receive the control signal or signals from the management system and the first and second clock signals from the clock generator, and further arranged to transmit the first and second clock signals to a supply generator when the control signal from the management system associated with the respective AC motor indicates that the motor is to be operated.
7. A system as claimed in any preceding claim, wherein the control system is a system for controlling the internal environment of a building.

-17 -
8. A method of operating a control system comprising a management system arranged to provide at least one control signal for at least one AC motor, the method comprising the steps of: S generating first and second clock signals that alternate between an off state and an on state, the first clock signal being in the off state when the second clock signal is in the on state; generating a power supply for the AC motor based upon the first and second clock signals when the control signal from the management system indicates that the AC motor is to be operated; wherein the power supply is at a first voltage level when the first clock signal is in the on state; wherein the power supply is at a second voltage level when the first clock signal is in the off state and the second clock signal is in the on state; and wherein the power supply is at a intermediate voltage level between the first and second voltage levels when the first and second clock signals are in the off state.
9. A method as claimed in claim 8, wherein the second clock signal is in the off state when the first clock signal is in the on state.
10. A method as claimed in claim 8 or 9, wherein the first clock signal is in the on state for a shorter period than it is in the off state.

-18 -
11. A method as claimed in any of claims 8 to 10, wherein the management system is arranged to provide a plurality of control signals each associated with a respective AC motor.
12. A method as claimed in claim 11, further comprising the steps of generating a power supply for each AC motor based upon the first and second clock signals when the associated control signal indicates that the AC motor is to be operated.
13. A method as claimed in any of claims 8 to 12, wherein the control system is for controlling the internal environment of a building.