Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
  • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
  • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using DC to AC converters or inverters
  • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using DC to AC converters or inverters with pulse width modulation
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
  • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
  • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
  • H02M7/5387—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
  • H02M7/53871—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
  • H02M7/53875—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output

Definitions

• the present invention relates to a variable speed electric motor drive system and method of compressor, a variable capacity compressor and a refrigeration system for the purpose of increasing the efficiency of frequency inverters employed in the drive.
• variable capacity compressors in refrigeration systems by activating the output stage (inverter bridge) active switches (eg MOSFETs) during the freewheeling interval of the motor current.
• variable capacity compressors which, as the name implies, allow adjustment of cooling capacity by varying the pumping speed of refrigerant gas (ie mass flow) according to the need of the system.
• variable capacity compressor performs the excursion from a minimum mass flow value to a maximum value by varying the speed of its motor.
• the variation of rotation is obtained by electronic control called frequency inverter, which adjusts voltage and frequency applied to the motor.
• Such a frequency inverter employs Pulse Width Modulation (PWM), that is, the voltage pulse width applied to the motor is controlled through a PWM modulator.
• PWM Pulse Width Modulation
• the PWM modulator sets the width (duration) of the pulse in proportion to the desired rotation, adjusting it according to the load and voltage of the supply network.
• the voltage applied to the motor is pulsed, with switching frequency usually of a few kHz.
• PWM modulation is applied to the motor phases by means of a inverter bridge, formed by the set of three arms, each responsible for applying voltage to one of the three phases of the motor.
• Each inverter bridge arm has two active solid state switches (IGBT or MOSFET type), referred to herein as active switches, each having in parallel a polarized passive solid state (DIO) switch, referred to herein as a passive, solid state switch. to drive current through the motor phases when the complementary active switch of the same arm is in cut-off state (open or not conducting current).
• IGBT active solid state switches
• DIO polarized passive solid state
• the power is transferred from the LINK DC to the electric motor.
• Electric current flows in the closed circuit formed by the LINK DC (usually composed of an energy storage stage obtained with an electrolytic capacitor), the upper active switch, a first phase of the electric motor, a second phase of the electric motor. , by the lower switch connected to this second phase, returning to the LINK DC.
• PWM modulation aims to adjust the instantaneous average voltage applied to the motor by measuring the voltage of the LINK DC over a period of time within the switching period, there are two main states: the first as already mentioned, where there is the transfer power to the motor, and the second where the upper active switch previously driving is cut (open), no longer transferring power to the motor. Electric current, however, continues to flow due to the inductive nature of the load (motor), finding a new circulation path through the same lower active switch and the passive switch (DIODE) parallel to the active switch complementary to that previously driven. Case If it does not reach zero, current will circulate in this circuit until the beginning of the next switching period where the upper active switch is again commanded to drive.
• DIODE passive switch
• This period when there is no energy transfer to the motor (where there is diode conduction) is known as the Freewheel stage of the motor current, in this range called the freewheel current. If the freewheel current reaches zero before the next switching period begins, the diode of this freewheel circuit will naturally block the current.
• PWM modulation follows a certain function in order to shape the voltage and fundamental current delivered to the motor.
• This function can be of different types (sinusoidal, rectangular, trapezoidal, etc.) depending on the type of motor and control.
• both IGBT type and MOSFET type active switches are employed.
• the freewheeling diode is purposely placed in parallel, usually within the same package as the active IGBT switch.
• MOSFET the freewheeling diode is naturally present in parallel with it, being a component with generally poor switching characteristics (slow switching diode), and conduction similar to that of the diode used with the IGBTs.
• the present invention aims, through the use of the Complementary PWM Modulation technique in frequency inverters employed in refrigeration systems equipped with variable capacity compressors:
• VDC variable capacity compressors
• the objectives of the present invention are achieved by employing the complementary actuation technique of the two active MOSFET-type switches of the same inverter bridge arm, a method also known as Complementary PWM Modulation, in frequency inverters employed to drive of variable capacity compressors.
• One way of translating the objectives of the present invention is by employing a known method of reducing conduction losses located in passive semiconductors (Diodes) that usually drive freewheeling currents.
• this method commonly referred to as “Complementary PWM Modulation”
• PWM modulation is employed in the operation of inverters present in high efficiency cooling systems, the system comprising an inverter bridge electrically associated with a variable speed electric motor. and triggered by a signal in PWM modulation, PWM modulation having two main stages identified by the time of energy transfer to the motor (or "T 0 N” period) and by the time period in which current free-wheeling (or "T O FF" period).
• the method employed with the main action is to activate the pair of active switches (MOSFETs) of the same arm, in a complementary way, causing the freewheel current not to circulate through the freewheeling diode, but through the channel of the switch.
• active MOSFET commanded to drive.
• variable speed electric motor drive system for compressor comprising an inverter bridge electrically associated with an electric motor, the inverter bridge being driven by a complementary PWM modulation.
• the complementary PWM modulation is driven at a substantially low electric motor speed relative to a reference speed, and the complementary PWM modulation is driven at a substantially low electric motor power relative to a reference power.
• a variable speed electric motor drive system for the compressor comprising an inverter bridge electrically associated with an electric motor, the inverter bridge being formed by active switches, the active switches being associated with one another. one in parallel with passive switches, each passive switch having two passive terminals, each active switch having two active terminals, each active switch forming a single encapsulation with its respective passive switch, the active switches driving in a adjustable driving time, the active switches going on as a function of a voltage between their active terminals substantially less than the voltage between the passive terminals of their respective passive switch.
• the objectives are achieved through a variable speed electric motor drive method for compressor, using an inverter bridge and an electric motor, comprising the following steps: obtaining a power signal from the electric motor, obtaining a electric motor speed signal, comparison of electric motor power signal with a reference power value, electric motor speed signal comparison with a reference speed value and inverter bridge drive via PWM modulation when the results of the rotation and power comparisons are below their respective reference values.
• variable capacity compressor powered by a drive system defined herein.
• Figure 1 illustrates an output stage of a frequency inverter with its most basic components.
• Figures 2a and 2b - is an example of conventional PWM drive showing the two main stages TON and TOFF and the path taken by the electric current in a modulation according to the state of the art;
• Fig. 3a and 3b is an example of complementary PW drive according to the present invention, showing the two main stages, illustrating that in the second stage (Fig. 2b) the freewheel chain is circulated through active switch, achieving loss reduction and meeting the objectives of the invention for refrigeration systems employing variable capacity compressors;
• Figures 4a and 4b shows the actuation signals of the three active switches involved in the example illustrated by figures 2a / 2b and 3a / 3b, with conventional PWM method and complementary PWM method to be employed;
• Figure 5 - illustrates the complementary drive applied to the three inverter bridge arms.
• Figure 1 exemplifies an output stage of a frequency inverter with its most basic components.
• the figure shows the inverter bridge 11 formed by six pairs of parallel associations of active and passive switches (see respectively Si, S ⁇ , S3, S 4 , S 5 , S 6 and Di, D 2 , D 3 , D 4 , D 5 , D 6 ), in which a PWM-type command signal is applied, which can assume the ON and OFF states in the respective time periods TON and TOFF. It also constitutes the basic circuit, a storage stage.
• the electric motor 10 is represented by the three inductive elements 1, 2 and 3, each representing one phase of the three phase motor.
• the inverter bridge shown in Figure 1 distributes to the motor phases the energy stored in the CLINK element, which receives power from an external source through classic elements not illustrated here (eg rectifier bridge connected to the mains power supply). alternating energy conversion stages connected to alternative energy sources, etc.).
• the inductive elements 1, 2 and 3 represent the electric motor 10 which drives, for example, a refrigerant gas compressor pump of the cooling system, or any other load to which the electric motor 10 is associated. It is clear, therefore, that actions to reduce loss by conduction of inverter bridge switches bring increased overall system efficiency.
• Figure 2a shows a conventional PWM loop.
• the power is transferred to the electric motor 10 through the path formed by the active switches ST and S 4 , for example of the MOSFET type switches, thus occurring energy losses located on both switches due to driving resistance of the same.
• the electric current naturally maintains its circulation through the passive switch D 2 (illustrated with an antiparallel diode at S 2 - see situation illustrated in figure 2b).
• the passive switch and active switch D 2 and S 4 respectively .
• a new cycle is started with the command for driving input of the active switch Si.
• Figures 3a and 3b comparatively illustrate figures 2a and 2b, the change that takes place in the sequence of actuation of the active switches to achieve the object of the present invention. It is shown that the first step does not differ from the one illustrated in figure 2 (see top), ie the same closed circuit for current circulation is maintained during power delivery to the electric motor 10, while also maintaining the same losses. by driving two active MOSFET switches. Already in the second main stage of the PWM, where the current circulates in freewheel, it is the deliberate actuation of the complementary switch to the one that previously opened, in the exemplified case, the actuation of S 2 . This allows the electric current to flow through the active switch channel S 2 instead of the passive switch D 2 .
• the electrical current will preferably flow through the active switch S 2 under conditions where the voltage drop between the terminals of this active switch S 2 is less than the voltage drop required for the passive switch D 2 to start driving.
• the current to be driven by the inverter bridge will be of low amplitude, and therefore obtainable. reducing the conduction losses by allowing electric current to flow through the active switches, ie through the MOSFET channel.
• figures 3a and 3b illustrate only the two main stages of the PWM switching period, the first one where the power transfer to the electric motor 10 is made (see figure 3a), and the second one where the current circulates in a wheel. -free (see figure 3b).
• Si the upper active switch
• S 2 the lower active switch of the same arm
• the upper active switches Si, S 3 and S 5 can be called first active switches and the lower switches S 2 , S 4 and S 6. , can be referred to as second active switches.
• the second (s) active switch (s) S 2 , S 4 , S 6 is powered ( (s) for a complementary TON-C feed time which should be slightly shorter than the TOFF off time of the first active switch (s) S ⁇ , S 3 , S 5 , it should preferably be established that the actuation of the second active switch (s) S 2 , S 4 , S 6 is only performed after a dead time T, such dead time TM being counted from turning off the first switch (s) Si, S 3 , S 5 .
• the minimum time interval TM also known as "De-ad-time" has as its main purpose to ensure that there are no simultaneous conduction of two switches of the same arm, ie, S 2 with Si, S4 with S 3. and S6 with S5, as such a situation would short the capacitor C L INK and possible permanent damage to the components involved.
• the other upper and lower switch combinations operate depending on the phases to which electrical power is to be delivered (for example, the same applies to sets S 3 , and S 4 ; S 5 , S 2 and S 6, Si, S 6 and S 2 , etc).
• Figures 4a and 4b demonstrate the actuation signals of the three active switches involved in the example illustrated by figures 2a / 2b and 3a / 3b, with conventional PWM method and complementary PWM method.
• the freewheeling current is shown to circulate through the MOS- FET when complementary modulation is used (supply occurring for a complementary time TON-C respecting the dead time T M also shown in figure 4b).
• the current through the S2 Drain is illustrated with negative polarity in the second frame of the figure to maintain the same polarity set for the active switch Si. The current, therefore, enters the active switch Source terminal S2 and exits through the Drain terminal thereof during the freewheeling period of the current, that is, by the complementary time TON-C previously interrupted by the path formed by Si.
• the complementary PWM modulation illustrated in figures 4a and 4b may or may not be maintained at different inverter operating points. Under higher load conditions, where the electric motor current is higher, the voltage between the conducting MOSFET terminals may be greater than the direct driving voltage of the freewheeling diode in parallel. In this situation, the current will naturally flow through the diode, regardless of the command given to the anti-parallel switch.
• a variable speed electric motor drive system for compressor comprises an inverter bridge 11 electrically associable with an electric motor 10, and the inverter bridge 11 is driven, as already mentioned, by a modulator. complementary PWM.
• Said complementary PWM modulation is driven, as will be described in more detail below, at a substantially lower electric motor speed 10 relative to a reference speed and a substantially lower electric motor power 10 relative to a reference power .
• the inverter bridge 11 of the present variable speed electric motor drive system for compressor is provided with active switches (Si, S 2 , S 3 , S 4 , S 5 , Se), associated one by one in parallel with passive switches ( Di, D 2 , D3, D 4 , D 5 , D 6 ), where each passive switch has two passive terminals and each active switch (Si, S 2 , S 3 , S 4 , S 5 , S 6 ) It has two active terminals.
• said passive switches are diode semiconductor devices.
• PWM modulation is formed by periods of time in which the active and passive switches are connected to an electric voltage (V M ) which is fed to the electric motor 0, said electric voltage (V) being connected for a period of time. Time (TON) and Off Time (TOFF) -
• the active switches (Si, S2, S3, S4, S5, SB) are electrically connected together in series and in pairs, to selectively and sequentially feeding the electric motor 0.
• the active and passive switches are associated with each other forming a group of first active switch (s) (Si, S 3 , S5) and a group of second active switch (s) ( S 2 , S 4 , Se).
• the first active switch (s) (Si, S 3 , S 5 ) are actuated in PWM modulation by the power on and off times. (T O NTOFF), where the system is configured so that the second active switch (s) (S 2 , S 4 , Se) respectively associated ⁇ ) in series and paired with the ) first active switch (s) (Si, S3, S5) are supplied during shutdown time (T 0 FF) of first switch (s) active (s) (Si, S 3 , S 5 ).
• each active and passive switch pair there is a single physical package or encapsulation.
• the active switches go into operation at an adjustable driving time, based on a voltage between their active terminals substantially less than the voltage between the passive terminals of their respective passive switch.
• a reference power is defined for the drive of the variable speed electric motor.
• I AVG I PK ⁇ (l - D)
• D - Cyclic ratio which depends mainly on rotation (the lower the rotation, the lower the cyclic ratio).
• a compressor motor has been tested in order to validate the presence of proposed and identify the optimum inverter bridge actuation points.
• the engine was driven at 1200 rpm and 1600 rpm.
• Complementary PWM modulation was developed at a switching frequency of 2.5 kHz.
• the tests were performed at an ambient temperature of 25 Q C using IRF840AS type MOSFET transistors.
• IRF840AS type MOSFET transistors.
• MOSFETS transistors of the type IRF840AS were used, however other types of transistors may be employed for the implementation of the inverter bridge.
• Tables 1 and 2 below allow a comparison between the efficiency achieved with the use of complementary PWM modulation (B) and that related to conventional modulation (A).
• the average current conducted by the passive switch (diode) and the effective current conducted by the active switch device (MOSFET transistor) depend on the amplitude of the current and its conduction time, which is why its values are directly influenced. by engine speed.
• the present variable speed electric motor drive system for the compressor is driven by complementary PWM modulation (applied to the inverter bridge 11) at the time the electric motor 10 operates at a substantially low speed relative to a reference speed.
• the reference rotation was determined around 2300 rpm, therefore, for rotation values below this reference, the efficiency increase obtained for the inverter bridge was verified.
• such drive is performed in an electric motor power 10 substantially low relative to a reference power determined on the basis of the IAVG and IRMS-
• FIG. 5 An example of the complementary PWM modulation method is shown in figure 5.
• the actuation sequence of the active switches for a brushless permanent magnet (or Brushless D Motor) application is shown. It is clear from the figure the complementary PWM modulation applied to the switch pairs S 1 , S2; S 3 , S 4 ; and S5 S 6.
• the constant cyclic ratio (TON OFF ratio) is maintained during the activation of each phase set of the electric motor 10.
• the complementary PWM modulation can be applied to variations of the exemplified case, where the ratio cyclic is adjusted according to any other temporal or discrete function, such as, for example, sinusoidal modulation of the cyclic ratio, or miscellaneous modulations applied to the cyclic ratio for load adjustments, compensations, etc.
• variable speed electric motor drive method for compressor using an inverter bridge 11 and an electric motor comprises the steps of:
• v. inverter bridge 1 1 is activated by a complementary PWM modulation when the results of comparisons iii and iv are below the reference values.
• the system is provided with an electronic control circuit (not shown) capable of controlling an electric motor 10 applicable, for example, to to a VDC variable capacity compressor via PW, controlled by an inverter bridge.
• the electronic control circuit In order to increase the efficiency of the cooling system, the electronic control circuit must be configured to drive the pair of active switches (MOSFETs) of the same arm, complementary (PWM complementary), causing the wheel current to free does not travel through the freewheeling diode, but through the active switch channel (MOSFET) commanding to drive.
• MOSFETs active switches
• PWM complementary complementary
• the object defined in the present invention as well as the results from the experimental test, prove that the overall efficiency of the cooling system is high with the reduction of conduction losses.
• the proposed motor drive PWM modulation particularly applied to compressors, offers greater reliability for the drive electronic circuit and the entire system in view of a lower operating temperature for the equipment.
• variable capacity compressor having a drive system according to the teachings of the present invention is provided, as well as a refrigeration system having the present drive system.
• the present invention presents a considerable increase in efficiency for refrigeration systems with the use of the complementary PWM methodology, when compared to that achieved by the solutions of prior art, notably by the use of conventional modulation.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Ac Motors In General (AREA)
• Inverter Devices (AREA)

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• 2008
  • 2008-10-28 BR BRPI0804620A patent/BRPI0804620B1/pt not_active IP Right Cessation
• 2009
  • 2009-10-28 DE DE112009002531T patent/DE112009002531T5/de active Pending
  • 2009-10-28 WO PCT/BR2009/000356 patent/WO2010048684A2/pt not_active Ceased
  • 2009-10-28 JP JP2011533491A patent/JP5643211B2/ja active Active
  • 2009-10-28 CN CN200980143022.0A patent/CN102204083B/zh active Active

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