GB2345353A

GB2345353A - Power supply apparatus for suppressing harmonics

Info

Publication number: GB2345353A
Application number: GB9914461A
Authority: GB
Inventors: Sun-Kill Yeom
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1998-12-30
Filing date: 1999-06-21
Publication date: 2000-07-05
Anticipated expiration: 2019-06-21
Also published as: KR100321244B1; CN1258958A; CN1148863C; GB9914461D0; KR20000045940A; GB2345353B

Abstract

A compressor 160 of an air conditioner is supplied from a power input 1 through a rectifier 100 and inverter 150. Power factor is controlled to reduce harmonics by short-circuiting the power line between the rectifier 100 and inverter 150 for time periods synchronised with zero crossings of the power input voltage and dependent on both the compressor drive frequency and the output of an outdoor temperature sensor which determines whether or not the compressor is in an overload condition.

Description

Power Supply Apparatus Description The present invention relates to an air conditioner with harmonic suppression apparatus and a method of harmonic suppression for an air conditioner.

A known air conditioner includes, as illustrated in Figure 1, a converter 3 for converting alternating current (AC) power input at power input terminals 1 to direct current (DC) power, a controller 5 for the operational frequency of a compressor 9 according to instructions based on outdoor conditions, an indoor unit to output an inverter driving signal and an inverter 7 for alternately turning on and turning off power transistors (not shown) according to a driving signal output by the controller 5 to convert the DC power output from the converter 3 to 3-phase AC power.

The converter 3 includes a bridge rectifier 11 for rectifying input AC power and a smoothing capacitor Cl connected between the output terminals of the bridge rectifier 11 for filtering out ripple components contained in the DC voltage output by the bridge rectifier 11.

In the inverter apparatus thus constructed, when input AC power is applied to the power input terminals 1, the AC input power is rectified by the bridge rectifier 11 and the ripple components contained in the DC power are filtered by the smoothing capacitor Cl.

The inverter 7 serves to alternately turn on and turn off six power transistors (not shown) according to a driving signal output by the controller 5 to convert the DC power output by the converter 3 to 3-phase (U-phase, V-phase, W-phase) AC power for driving the compressor 9.

The converter 3 utilises a relatively large value smoothing capacitor C1 in order to obtain a DC having small ripples. However there is a problem in that the input current is distorted by the influence of the smoothing capacitor Cl into a non-sinusoid waveform which increases its harmonic components. As a result, operational problems with the power capacitor, circuit breakers and the like occur and reduces the power factor.

European and other advanced countries have standards and specifications (EN 55022) for such harmonics which follow recommendations of International Electrotechnical Commission (IEC).

Accordingly, an air conditioner should be designed to satisfy the harmonic standard (EN 55022). When the inverter 7 is switched on to drive the compressor 9, harmonic components are conspicuously increased necessitating development of a harmonic suppressing apparatus.

Referring to Figure 2, a known harmonic suppressing apparatus for an air conditioner comprises a zero crossing detector 13 and a harmonic suppresser 15 in addition to the conventional inverter apparatus of Figure 1. The zero crossing detector 13 detects the voltage zero crossing points of AC input power from the power input terminals 1 and inputs a pulse signal to the controller 3 for each voltage zero crossing point. The harmonic suppresser 15 short circuits a positive (+) power line and a negative (-) power line at the trailing edges of the pulse signals from the zero crossing detector 13 for a harmonic suppress period set up in the controller 3.

In the harmonic suppressing apparatus of an air conditioner thus constructed, when AC input power is supplied from the power input terminals 1, the AC input power is converted to DC power by the converter 3 and the inverter 7 alternately turns on and turns off the six power transistors (not shown) according to the driving signal from the controller 5 to convert the DC power output from the converter 3 to 3-phase (U-phase, V-phase, Wphase) AC power for driving the compressor 9.

When the compressor 9 is rendered active, current waveform (b) lags behind the voltage in proportion to the amount of current flowing through the load (the compressor), such that, as shown in Figure 4, there is generated a phase difference between the current waveform (b) and voltage waveform (a) which increases the harmonic components.

Accordingly, in order to remove the harmonic components, the zero voltage points of the AC input power from the power input terminal 1 is detected by the zero crossing detector 13 and inputs a pulse signal (c) (Figure 3) to the controller 5 at the zero crossings of the voltage waveform (a).

The controller 5 drives the harmonic suppresser 15 at a trailing edge of the pulse signal (c) for a predetermined harmonic suppressing period during which the positive (+) power line and the negative (-) power line that connect the converter 3 to the inverter 7 are short circuited to make a pulse in the current waveform (b), as shown in Figure 5, thereby decreasing the phase difference between the current waveform (b) and the voltage waveform (a) and suppressing the harmonic components.

When the compressor 9 is being operated at a low frequency, the current is also reduced to decrease the phase difference between the current waveform (b) and the voltage waveform (a), and when the compressor 9 is operated at a high frequency, the current is also increased to widen the phase difference between the voltage waveform (a) and the current waveform (b). Therefore, the controller 5 establishes a harmonic suppressing time in proportion to the operation frequency of the compressor 9.

When the harmonic suppressing time established at the controller 5 according to the operation frequency of the compressor 9 has elapsed, the harmonic suppresser 15 is turned off.

However, there is a problem with the above-described harmonic suppressing apparatus in that the harmonic components cannot be effectively suppressed when operation is executed under overload conditions because the harmonic suppresser 15 is activated during a harmonic suppression period established only in proportion to the operational frequency of the compressor 9 without considering that the phase difference between the voltage waveform (a) and current waveform (b) during overload conditions becomes even larger, as illustrated in Figure 6.

According to the present invention, there is provided a power supply apparatus comprising an AC to DC converter, a DC to AC inverter for converting the output of the AC to DC converter into AC and supplying said AC to a load and power factor control means, wherein the power factor control means includes a zero crossing detector for detecting voltage zero crossings in AC input to the AC to DC converter, load determining means for determining the load on the apparatus and shorting means for temporarily shorting the output of the AC to DC converter in response to detected voltage zero crossings in AC input to the AC to DC converter for a period determined in dependence on the determined load The power factor control means serves to keep the power factor within acceptable bounds and consequently controls harmonic generation.

The inverter may output 3-phase AC.

The inverter may be responsive to a control signal to vary the frequency of its output. In this case, the shorting means preferably varies said period in dependence on the frequency of the inverters output. This may be achieved by the shorting means including a ROM table mapping inverter output frequency to control values for said period.

The load determining means may indirectly determine the electrical load on the apparatus.

For instance, in an air conditioner including a compressor powered by an apparatus according the present invention, the load determining means could be an outdoor temperature sensor.

An embodiment of the present invention will now be described, by way of example, with reference to Figures 7 to 10 of the accompanying drawings in which : Figure 1 is a circuit block diagram of a known inverter apparatus; Figure 2 is a block diagram of a known harmonic suppressing apparatus; Figure 3 is a waveform diagram of a pulse output from a voltage zero crossing point detector, Figure 4 is a voltage and current waveform diagram before the known harmonic suppresser is driven ; Figure 5 is a voltage and current waveform diagram when the known harmonic suppresser is in use; Figure 6 is a voltage and current waveform diagram under overload and normal load conditions when the known harmonic suppresser is in use; Figure 7 is a block diagram of a harmonic suppressing apparatus of an air conditioner according to the present invention; Figure 8 is a detailed circuit diagram of the harmonic suppressing apparatus of Figure 7; Figure 9 is a flow chart for illustrating the harmonic suppressing operational procedure of the air conditioner of Figure 7; and Figure 10 is a voltage and current waveform diagram for overload and normal load conditions when employing an embodiment of the present invention.

Referring to Figures 7 and 8, converter means 100 rectifies and smoothes AC input power from power input terminals 1. Voltage zero crossing detecting means 110 includes a filtering unit 112, a photocoupler 114, a first switching unit 116 and a second switching unit 118 and detects voltage zero crossing points in the AC input power.

The filtering unit 112 comprises resistors R1, R2 and capacitors Cl, C2 for filtering noise from the AC input power. The photocoupler 114 receives the filtered AC input power from the filtering unit 112.

The first switching unit 116 comprises resistors R3"R6, a transistor TR1 and a capacitor C3 and receives a voltage Vccl. The second switching unit 118 includes resistors R7" R10, a transistor TR2 and a capacitor C4.

Outdoor temperature detecting means 120 serves to detect the outdoor temperature and includes an outdoor temperature sensor 122 whose resistance value changes according to the outdoor temperature, a resistor R15 which forms a potential divider with the outdoor temperature sensor 122, a capacitor C9 for filtering noise components contained in the signal at the node between the resistor R15 and the outdoor temperature sensor 122, and a resistor R16 connecting the node between the resistor R15 and the outdoor temperature sensor 122 to control means (described later).

Control means 130 is a microcomputer which is synchronised with a zero crossing point signal (pulse signal) for the AC input power from the zero crossing detecting means 110 to output a control signal such that the phase of the input current from the power input terminals 1 approaches the phase of input voltage and which determines an operational frequency for a compressor 160 according to commands from an indoor unit and the outdoor conditions and outputs an appropriate inverter driving signal. The control means 130 stores, in a read only memory (ROM) table, basic control values (harmonic suppression times) which change in proportion to the operational frequency of the compressor 160.

The control means 130 also determines whether the outdoor temperature detected by the outdoor temperature detecting means 120 corresponds an overload condition or a normal load condition and modifies the harmonic suppressing time stored in the ROM table in dependence thereon.

Harmonic suppressing means 140 receives a switching signal from the control means 130 and comprises a third switching unit 142, a hybrid integrated circuit element 144 (hereinafter referred to as"hybrid element") and a power switching unit 146.

The third switching unit 142 includes capacitors C5'C8, resistors R11 ~ R13, a transistor TR3 and a diode Dl arranged such that it can supply a current to the hybrid element 144 according to a control signal of high level output by the control means 140. The hybrid element 144 receives the current from the third switching unit 142 and output a voltage signal of high level in response thereto.

Power switching unit 146 includes a resistor R14, a transistor TR4, a diode D4 and power noise eliminating choke transformers L1, L2 arranged such that it short circuits a positive (+) power line and a negative (-) power line connecting inverter means (described later) and the converter means 100 in response to a voltage signal of high level input from the hybrid element 144.

The inverter means 150 alternately turns on and turns off 6-power transistors (not shown) according to a driving signal output from the control means 130 to convert the DC power output from the converter means 100 to variable frequency 3-phase AC (U-phase, V-phase, W-phase) suitable for the operational frequency of the compressor 160 and supplies the same to the compressor 160.

The operation of the harmonic suppressing apparatus of an air conditioner thus constructed and the suppression method thereof will now be described.

When AC power is supplied from the power input terminals 1, the input AC power is converted to DC power by the converter means 100, and the inverter means 150 turns on and turns off the 6 power transistors (not shown) according to the driving signal output from the control means 130 to convert the DC power output from the converter means 100 to 3-phase AC power and to drive the compressor 160.

When the compressor 160 is driven, the current waveform (b) lags behind the voltage waveform (a), as shown in Figure 4, creating harmonic components.

In the present invention, the zero crossing detecting means 110, outdoor temperature detecting means 120, control means 130 and harmonic suppressing means 140 are constructed, and control is performed to make the current phase approach the voltage phase, as illustrated in Figure 5.

Referring to Figure 9, first of all, at step S1, the control means 130 reads basic data (driving time) for the harmonic suppressing means 140 for increasing or decreasing the harmonic suppressing time (t) according to the operational frequency of the compressor 160 from the ROM table. When the operation frequency of the compressor 160 is decreased, the value of the basic data at the harmonic suppressing means 140 shortens the driving time of the harmonic suppressing means 140 because the consumed current is also reduced thereby reducing the phase difference between the voltage waveform and the current waveform and when the operational frequency of the compressor 160 is increased, the consumed current is also increased thereby increasing the phase difference between the voltage waveform and the current waveform and consequently the driving time of the harmonic suppressing means 140 is lengthened to control the harmonic suppressing time (t).

At step S2, the control means 130 determines an operation frequency for the compressor 160 according to the outdoor conditions and the command from the indoor unit. Atthis moment, the power noise component of the input AC power from the power input terminals 1 is removed by the filtering unit 112 and the AC power is applied to the photocoupler 114 of the zero crossing detecting means 110.

At voltage zero crossings, the transistor TR1 is turned on and the transistor TR2 is turned off and a pulse signal (c) synchronous with a zero potential point of the AC input power is input to the control means 130 from the zero crossing detecting means 110, as shown in Figure 3.

At step S3, a determination is made as to whether the zero crossing pulse signal (c) is being input to the control means 130, and if the zero crossing pulse signal (c) is not being input (in case of NO), operations subsequent to step S3 are repeatedly performed until the zero crossing pulse signal (c) is input.

As a result of the determination at step S3, if the zero crossing pulse signal (c) is being input (In case of YES), flow proceeds to step S4 for detection of the output of the outdoor temperature detecting means 120.

At step S5, the control means 130 converts the analogue voltage input from the outdoor temperature detecting means 120 to digital data and determines whether the outdoor temperature represents an overload or a normal load condition.

The existence of an overload or a normal load condition is established according to the characteristics of the air conditioner and its installation such that, by way of example, when the outdoor temperature is over 40 degrees Celsius, it is determined that an overload condition exists.

The overload condition can be subdivided. By way of example, when the outdoor temperature is in the range 40 ' 45 during cooling operation, it is called a first overload condition, when it is over 45 , it is called as a second overload condition.

As a result of the determination at step S5, if the outdoor temperature meets the overload condition (in case of YES), flow advances to step S6, where the control means 130 increases by At the basic data value (t) of the harmonic suppressing means 140 read from the ROM table, that is, increases the driving time of the harmonic suppressing means 140 as much as increased consumed current.

As a result of the determination at step S5, if the outdoor temperature meets the normal load condition (in case of NO), flow proceeds to step S7, where the control means 130 determines a driving time (t) for the harmonic suppressing means 140 corresponding to the operational frequency of the compressor 160 read from the ROM table at step S1.

When the driving time of the harmonic suppressing means 140 is determined according to the discrimination as to whether the outdoor temperature is an overload or a normal load condition, flow proceeds to step S8, where the control means 130 outputs to the harmonic suppressing means 140 a control signal of high level for driving the harmonic suppressing means 140 during the harmonic suppressing time determined by the outdoor temperature at a trailing edge of the pulse signal (c) input from the zero potential detecting means 110.

Then, the harmonic suppressing means 140 turns on the transistor TR3 at the third switching unit 142 according to the control signal of high level input from the control means 130 to supply a current to the hybrid element 144 and to thereby short-circuit the positive (+) power line and the negative (-) power line connecting the converter means 100 and the inverter means 150.

When the positive (+) power line and the negative (-) power line are short-circuited, a current waveform is formed during a short period of time, such that the phase difference between the current waveform (b) and the voltage waveform (a) is narrowed to suppress the harmonic components.

At the same time, in consideration of the fact that the phase difference between the voltage waveform (a) and current waveform (b') during the overload becomes larger than the phase difference between the voltage waveform (a) and than current waveform (b) under normal load even though the compressor 160 is operated on the same operation frequency, the phase difference between the voltage waveform (a) and the current waveform (b) is made smaller during the overload by increasing the harmonic suppressing time when the outdoor temperature represents an overload condition.

Accordingly, the harmonic components are effectively suppressed regardless of the load changes to enable a control operation of sufficiently meeting the current harmonic regulations of EN 55022, such that the harmonic suppressing means can be used on harmonic apparatus of all electronic devices utilising an inverter method.

As apparent from the foregoing, there is an advantage in the harmonic suppressing apparatus of an air conditioner and suppressing method thereof according to the present invention thus described in that an outdoor temperature is detected to discriminate whether the harmonic suppressing time more in overload condition, and to increase a harmonic suppressing time more in overload condition than in normal load condition, such that standard of EN 55022 can be met to limit the harmonic current regardless of load changes.

Claims

Claims 1. A power supply apparatus comprising an AC to DC converter, a DC to AC inverter for converting the output of the AC to DC converter into AC and supplying said AC to a load and power factor control means, wherein the power factor control means includes a zero crossing detector for detecting voltage zero crossings in AC input to the AC to DC converter, load determining means for determining the load on the apparatus and shorting means for temporarily shorting the output of the AC to DC converter in response to detected voltage zero crossings in AC input to the AC to DC converter for a period determined in dependence on the determined load 2. An apparatus according to claim 1, wherein the inverter outputs 3-phase AC.

3. An apparatus according to claim 1 or 2, wherein the inverter is responsive to a control signal to vary the frequency of its output.

4. An apparatus according to claim 3, wherein the shorting means varies said period in dependence on the frequency of the inverters output.

5. An apparatus according to claim 4, wherein the shorting means includes a ROM table mapping inverter output frequency to control values for said period.

6. An apparatus according to any preceding claim, wherein the load determining means indirectly determines the electrical load on the apparatus.

7. An air conditioner including a compressor powered by an apparatus according to claim 6, wherein the load determining means comprises an outdoor temperature sensor.

8. A harmonic suppressing apparatus of an air condition, the air conditioner including converter means for converting an AC input power of power input terminal to a DC power, inverter means for converting the DC power converted at the converter means to a 3-phase AC power of desired frequency and a compressor which is rotated by the 3-phase AC power output from the inverter means, wherein the apparatus comprises: zero potential detecting means for detecting a zero potential point of input voltage from the power input terminal; outdoor temperature detecting means for detecting an outdoor temperature; control means for discriminating whether the outdoor temperature detected by the outdoor temperature detecting means is an overload or a normal load condition, and for increasing harmonic suppressing time more than in the normal condition if the outdoor temperature is the overload condition; and harmonic suppressing means for synchronizing with the zero potential point of the input voltage input from the zero potential detecting means to thereby short-circuit a power line of the compressor.

9. The apparatus as defined in claim 8, wherein the harmonic suppressing means short-circuit a plus (+) power line and a minus (-) power line connecting the converter means and the inverter means during a harmonic suppressing time determined by the control means.

10. The apparatus as defined in claim 8, wherein the control means stores a basic control value which proportionally controls a driving time of the harmonic suppressing means according to operation frequency of the compressor and changes the basic control value according to outdoor temperature detected by the outdoor temperature detecting means.

11. A harmonic suppressing apparatus of an air condition, the apparatus including converter means for converting an AC input power of power input terminal to a DC power, inverter means for converting the DC power converted at the converter means to a 3-phase AC power of desired frequency and a compressor which is rotated by the 3-phase AC power output from the inverter means, wherein an apparatus for suppressing harmonic components by way of reducing a phase difference between an input current and an input voltage,comprises: zero potential detecting means for detecting a zero potential point of an input voltage input from the power input terminal; outdoor temperature detecting means for detecting an outdoor temperature; control means for outputting a control signal in order to allow a phase of an input current to synchronize with a zero potential point of an input voltage input from the zero potential detecting means and to approach a phase of the input voltage; and harmonic suppressing means for shortcircuiting a power line of the compressor in order to allow a phase of input current to approach a phase of input voltage according to the control signal output from the control means, wherein the control means discriminates whether an outdoor temperature detected by the outdoor temperature detecting means is an overload or a normal load condition, and, if the outdoor temperature is the overload condition, increases a driving time of the harmonic suppressing means more than in the normal load condition.

12. A harmonic suppressing method of air conditioner adapted for converting an AC power output from the power input terminal to a DC power and converting the converted DC power to a 3-phase AC power of desired frequency to thereafter operate a compressor, the method comprising the steps of : establishing a driving time of harmonic suppressing means proportionate to operation frequency of the compressor; detecting a zero potential point of input voltage input from the power input terminal; detecting an outdoor temperature to discriminate whether the outdoor temperature is an overload or a normal load ; shortcircuiting the power line of the compressor for a time period more increased than driving time of the harmonic suppressing means established at the time establishing step when the outdoor temperature is overload condition at the overload discriminating step; and shortcircuiting the power line of the compressor for a driving time of the harmonic suppressing means established at the time establishing step when the outdoor temperature is normal load at the overload discriminating step.

13. The method as defined in claim 12, wherein the harmonic suppressing step during the overload and the normal load further includes the step of synchronizing with a zero potential point of the input voltage detected at the zero potential detecting step to thereby short-circuit a power line of the compressor. 14. An air conditioner substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

Amendments to the claims have been filed as follows Claims 1. A power supply apparatus comprising an AC to DC converter, a DC to AC inverter for converting the output of the AC to DC converter into AC and supplying said AC to a load and power factor control means for harmonic suppression, wherein the power factor control means includes a zero crossing detector for detecting voltage zero crossings in AC input to the AC to DC converter, load determining means for determining the load on the apparatus and shorting means for temporarily shorting the power supply to the load in response to detected voltage zero crossings in AC input to the AC to DC converter for a period determined in dependence on the determined load.
2. An apparatus according to claim 1, wherein the inverter outputs 3-phase AC.
3. An apparatus according to claim 1 or 2, wherein the inverter is responsive to a control signal to vary the frequency of its output.
4. An apparatus according to claim 3, wherein the shorting means varies said period in dependence on the frequency of the inverters output.
5. An apparatus according to claim 4, wherein the shorting means includes a ROM table mapping inverter output frequency to control values for said period.
6. An apparatus according to any preceding claim, wherein the shorting means shorts the power supply to the load at the output of the AC to DC converter.
7. An apparatus according to any preceding claim, wherein the load determining means indirectly determines the electrical load on the apparatus.
8. An air conditioner including a compressor powered by an apparatus according to claim 7, wherein the load determining means comprises an outdoor temperature sensor.
9. An air conditioner substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

9. An air conditioner substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

**WARNING** end of CLMS field may overlap start of DESC **.

**WARNING** start of DESC field may overlap end of CLMS **.

Amendments to the claims have been filed as follows Claims 1. A power supply apparatus comprising an AC to DC converter, a DC to AC inverter for converting the output of the AC to DC converter into AC and supplying said AC to a load and power factor control means for harmonic suppression, wherein the power factor control means includes a zero crossing detector for detecting voltage zero crossings in AC input to the AC to DC converter, load determining means for determining the load on the apparatus and shorting means for temporarily shorting the power supply to the load in response to detected voltage zero crossings in AC input to the AC to DC converter for a period determined in dependence on the determined load.

2. An apparatus according to claim 1, wherein the inverter outputs 3-phase AC.

3. An apparatus according to claim 1 or 2, wherein the inverter is responsive to a control signal to vary the frequency of its output.

4. An apparatus according to claim 3, wherein the shorting means varies said period in dependence on the frequency of the inverters output.

5. An apparatus according to claim 4, wherein the shorting means includes a ROM table mapping inverter output frequency to control values for said period.

6. An apparatus according to any preceding claim, wherein the shorting means shorts the power supply to the load at the output of the AC to DC converter.

7. An apparatus according to any preceding claim, wherein the load determining means indirectly determines the electrical load on the apparatus.

8. An air conditioner including a compressor powered by an apparatus according to claim 7, wherein the load determining means comprises an outdoor temperature sensor.