Abstract:
Variable frequency drive active harmonic mitigation controls and diagnostics are disclosed. Exemplary controls and diagnostics include operating a variable frequency drive including converting an AC input line voltage to a DC voltage, generating a motor drive signal using the DC voltage, and driving an electric motor with the motor drive signal. A harmonic mitigation signal is provided to the drive configured to at least partially mitigate harmonics during the operation of the drive. The harmonic mitigation signal is inhibited based upon presence of an error condition associated with the drive input. The inhibiting is terminated based upon the absence of the error condition. A diagnostic fault condition based upon a number of occurrences of the error condition.

Description:
BACKGROUND 
       [0001]    Variable frequency drives offer a number of potential advantages for heating, ventilation, air conditioning, or refrigeration (HVACR) applications including opportunities for enhanced efficiency, control, and performance. Yet they also pose a number of design challenges including the need to mitigate harmonic losses due to power line input harmonic currents and/or terminal voltages. Various techniques have been proposed to mitigate harmonics including link chokes, line reactors, multiphase techniques, harmonic filters, and combinations of these and other techniques. Active harmonic attenuation, cancellation or damping techniques may also be used to mitigate harmonics. These and other active harmonic mitigation (“AHM”) techniques generally utilize controls which analyze a given drive signal for the presence and characteristics of harmonic distortion and generate a mitigation command or signal configured to provide desired attenuation, cancellation or damping to produce a desired corrected drive signal, for example, to produce a more precise synthesized approximation of a sinusoid, or to mitigate harmonic feedback to the input or output of a variable frequency drive. They may be implemented alone or in combination with other techniques. While AHM techniques offer a number of potential benefits, they also present a number of unanticipated challenges and problems with respect to HVACR applications. Various duty cycle requirements of HVACR applications can give rise to control states that, while desirable from a harmonic mitigation perspective, have the potential to damage the system. These issues may be of particular interest in applications utilizing permanent magnet motors though they are broadly applicable to other systems as well. There is a significant need for the unique and inventive apparatuses, methods and systems disclosed herein. 
       DISCLOSURE 
       [0002]    For the purposes clearly, concisely and exactly describing exemplary embodiments of the invention, the manner and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain exemplary embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall be understood that no limitation of the scope of the invention is thereby created, and that the invention includes and protects such alterations, modifications, and further applications of the exemplary embodiments as would occur to one skilled in the art to which the invention relates. 
       SUMMARY 
       [0003]    Apparatuses, methods and systems for control and diagnostics of variable frequency drive active harmonic mitigation are disclosed. Exemplary controls and diagnostics include operating a variable frequency drive which converts an AC input line voltage to a DC voltage, generates a motor drive signal using the DC voltage, and drives an electric motor with the motor drive signal. A harmonic mitigation signal is provided to the drive and is configured to at least partially mitigate harmonics during the operation of the drive. The harmonic mitigation signal is inhibited based upon presence of an error condition associated with the drive input. The inhibiting is terminated based upon the absence of the error condition. A diagnostic fault condition is based upon a number of occurrences of the error condition. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0004]      FIG. 1  is a schematic of an exemplary HVACR system. 
           [0005]      FIG. 2  is a schematic of an exemplary variable frequency drive and permanent magnet motor. 
           [0006]      FIGS. 3 and 4  are flow diagrams illustrating exemplary control and diagnostic processes. 
           [0007]      FIG. 5  is a block diagram illustrating exemplary controls and diagnostics. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    With reference to  FIG. 1  there is illustrated an exemplary HVACR system  100  which includes a refrigerant loop comprising a compressor  110 , a condenser  120 , and an evaporator  130 . Refrigerant flows through system  100  in a closed loop from compressor  110  to condenser  120  to evaporator  130  and back to compressor  110 . Various embodiments may also include additional refrigerant loop elements including, for example, valves for controlling refrigerant flow, refrigerant filters, economizers, oil separators and/or cooling components and flow paths for various system components. 
         [0009]    Compressor  110  is driven by a drive unit  150  including a permanent magnet electric motor  170  which is driven by a variable frequency drive  155 . In the illustrated embodiment, variable frequency drive  155  is configured to output a three-phase PWM drive signal, and motor  170  is a surface magnet permanent magnet motor. Use of other types and configurations of variable frequency drives and permanent magnet electric motors such as interior magnet permanent magnet motors are also contemplated. It shall be appreciated that the principles and techniques disclosed herein may be applied to a broad variety of drive and motor configurations including inductance motor systems, reluctance motor systems and other motor systems. 
         [0010]    Condenser  120  is configured to transfer heat from compressed refrigerant received from compressor  110 . In the illustrated embodiment condenser  120  is a water cooled condenser which receives cooling water at an inlet  121 , transfers heat from the refrigerant to the cooling water, and outputs cooling water at an output  122 . It is also contemplated that other types of condensers may be utilized, for example, air cooled condensers or evaporative condensers. It shall further be appreciated that references herein to water include water solutions comprising additional constituents unless otherwise limited. 
         [0011]    Evaporator  130  is configured to receive refrigerant from condenser  120 , expand the received refrigerant to decrease its temperature and transfer heat from a cooled medium to the refrigerant. In the illustrated embodiment evaporator  130  is configured as a water chiller which receives water provided to an inlet  131 , transfers heat from the water to the refrigerant, and outputs chilled water at an outlet  132 . It is contemplated that a number of particular types of evaporators and chiller systems may m be utilized, including dry expansion evaporators, flooded type evaporators, bare tube evaporators, plate surface evaporators, and finned evaporators among others. 
         [0012]    HVACR system  100  further includes a controller  160  which outputs control signals to variable frequency drive  155  to control operation of the motor  170  and compressor  110 . Controller  160  also receives information about the operation of drive unit  150 . In exemplary embodiments controller  160  receives information relating to motor current, motor terminal voltage, and/or other operational characteristics of the motor including those described herein below. It shall be appreciated that the controls, control routines, and control modules described herein may be implemented using hardware, software, firmware and various combinations thereof and may utilize executable instructions stored in a non-transitory computer readable medium or multiple non-transitory computer readable media. It shall further be understood that controller  160  may be provided in various forms and may include a number of hardware and software modules and components such as those disclosed herein. Furthermore, it shall be appreciated that controller  160  is one example of a controller which may be configured to implement the exemplary controls and diagnostics disclosed herein, in whole or in part in combination with other systems, modules or components. 
         [0013]    With reference to  FIG. 2  there is illustrated an exemplary circuit diagram for a variable frequency drive  200 . Drive  200  is connected to a power source  210 , for example, a 400/480 VAC utility power supply which provides three-phase AC power to line filter module  220 . Line filter module  220  is configured to provide a sync signal and serve as an RF filter. Three-phase AC power is then provided to a rectifier  290  which converts the AC power to DC power and provides the DC power to a DC to bus  291 . The DC bus is connected to inverter  280 . For clarity of illustration and description, rectifier  290 , DC bus  291 , and inverter  280  are shown as discrete blocks. It shall be appreciated, however, that two or more of these components may be provided in a common module, board or board assembly which may also include a variety of additional circuitry and components. In addition to the illustrated 6-pulse configuration, it shall be further understood that multiple pulse rectifiers such as 12-pulse, 18-pulse, 24-pulse or 30-pulse rectifiers may be utilized along with phase shifting transformers providing appropriate phase inputs for 6-pulse 12-pulse, 18-pulse, 24-pulse, or 30-pulse operation. 
         [0014]    Inverter module  280  includes switches  285 ,  286  and  287  which are connected to the positive and negative lines of the DC bus  291 . Switches  285 ,  286  and  287  are preferably configured as IGBT and diode based switches, but may also utilize other types of power electronics switching components such as power MOSFETs or other electrical switching devices. Switches  285 ,  286  and  287  provide output to motor terminals  275 ,  276  and  277 . Current sensors  281 ,  282  and  283  are configured to detect current flowing from inverter module  280  to motor  270  and send current information to ID module  293 . Voltage sensors are also operatively coupled with motor terminals  275 ,  276  and  277  and configured to provide voltage information from the motor terminals to ID module  293 . 
         [0015]    ID module  293  includes burden resistors used in connection with current sensing to set the scaling on current signals ultimately provided to analog to digital converters for further processing. ID module  293  tells the VFD what size it is (i.e. what type of scaling to use on current post ADC) using identification bits which are set in hardware on the ID module  293 . ID module  293  also outputs current and voltage information to gate drive module  250  and also provides identification information to gate drive module  250  which identifies the type and size of the load to which gate drive module  250  is connected. ID module  293  may also provide current sensing power supply status information to gate drive module  250 . ID module  293  may also provide scaling functionality for other parameters such as voltage or flux signals in other embodiments. 
         [0016]    Gate drive module  250  provides sensed current and voltage information to analog to digital converter inputs of DSP module  260 . DSP module  260  processes the sensed current and voltage information and also provides control signals to gate drive module  250  which control signals gate drive module  250  to output voltages to boost modules  251 ,  252  and  253 , which in turn output boosted voltages to switches  285 ,  286  and  287 . The signals provided to switches  285 ,  286  and  287  in turn control the output provided to terminals  275 ,  276  and  277  of motor  270 . It shall be appreciated that DSP module  260  is one example of a controller which may be configured to implement the exemplary controls and diagnostics disclosed herein, in whole or in part in combination with other systems, modules or components. 
         [0017]    Motor  270  includes a stator  271 , a rotor  273 , and an air gap  272  between the rotor and the stator. Motor terminals  275 ,  276  and  277  are connected to windings provided in stator  271 . Rotor  273  includes a plurality of permanent magnets  274 . In the illustrated embodiment magnets  274  are configured as surface permanent magnets positioned about the circumference of rotor  273 . The rotor is typically constructed using the permanent magnets in such a way as essentially a constant magnetic flux is present at the surface of the rotor. In operation with rotation of the rotor, the electrical conductors forming the windings in the stator are disposed to produce a sinusoidal flux linkage. Other embodiments also contemplate the use of other magnet configurations such as interior magnet configurations. It shall be understood that interior magnet configurations typically have different inductances in the q-axis and the d-axis. 
         [0018]    With reference to  FIG. 3  there is illustrated a flow diagram of an exemplary control and diagnostic process  300 . Process  300  begins at operation  302  which initializes an active harmonic mitigation (“AHM”) control process which is configured and executable to mitigate power line input harmonic currents and/or terminal voltages. From operation  302  process  300  proceeds to conditional  304  which evaluates whether a frequency F, such as the drive input line frequency, is above a minimum frequency MinF and below a maximum frequency MaxF. If conditional  304  returns false, process  300  proceeds to operation  306  which inhibits the AHM process. From operation  306  process  300  proceeds to operation  308  which tests whether a frequency range error FRE is greater than a threshold for frequency range errors THFRE. If conditional  308  returns false, process  300  proceeds to conditional  342 . If conditional  308  returns true, process  300  proceeds to operation  310  which sets a diagnostic fault DFRE equal to true and proceeds to conditional  342 . Conditional  342  tests whether the number of inhibit operations is greater than a limit on the number of inhibit operations Linhibit. If conditional  342  returns true, process  300  proceeds to operation  302  which reinitializes the AHM process or sends a signal indicating that a manual reset is needed. If conditional  342  returns false, process  300  returns to conditional  304 . If conditional  304  returns true, process  300  proceeds to operation  312  which sets diagnostic DFRET equal to false. From operation  312  process  300  proceeds to operation  314  which tests for a lost sync signal condition. If conditional  314  returns true, process  300  proceeds to operation  316  which inhibits the AHM process. From operation  316  process  300  proceeds to conditional  318  which tests whether the number of sync signal errors SSE is greater than a threshold THSSE. If conditional  328  returns false, process  300  proceeds to conditional  342 . If conditional  328  returns true, process  300  proceeds to operation  330  which sets diagnostic fault code DSSE equal to true. From operation  330  process  300  proceeds to conditional  342 . If conditional  342  returns false, process  300  proceeds to operation  340  which sets diagnostic fault code DSSE equal false. From operation  340  process  300  proceeds to conditional  342 . 
         [0019]    With reference to  FIG. 4  there is illustrated a flow diagram according to an exemplary control and diagnostic process  400 . Process  400  begins at operation  402  which initializes an AHM process. From operation  402 , process  400  proceeds to conditional  404 . Conditional  404  tests for a frequency error, a delta frequency error, a line voltage imbalance error, and/or an short term electrical disturbance error, such as an electrical transient, a voltage surge, a ring wave, an electrical fast transient burst, an RF conducted immunity, a voltage variation, a voltage dip, a voltage interruption, or a voltage notch among others. If conditional  404  returns false, process  400  proceeds to conditional  412 . If conditional  404  returns true, process  400  proceeds to operation  406  which inhibits the AHM process. From operation  406  process  400  proceeds to operation  408  which tests whether a diagnostic limit has been reached for the frequency error, the delta frequency error, the line voltage imbalance error, and/or the electrical transient error. If operation  408  returns false, process  400  proceeds to conditional  412 . If conditional  408  returns true, process  400  proceeds to operation  410  which sets a diagnostic fault code. From operation  410  process  400  proceeds to conditional  412 . Conditional  412  tests whether a limit on the number of inhibit operations has been reached. If conditional  412  returns true, process  400  returns to operation  402  which reinitializes the AHM process or sends a signal that a manual reset is needed. If conditional  412  returns false, process  400  returns to conditional  404 . 
         [0020]    With reference to  FIG. 5  there is illustrated a block diagram of exemplary AHM controls  500 . Block  550  illustrates the inputs that are provided to line sync algorithm  530  and AHM algorithm  510  which include the amplitude, frequency, source impedance, external loads, waveshapes, noise and transients of the input line voltage provided to a variable frequency drive. Line synch algorithm  530  utilizes the input information to provide synchronization information, for example, information indicating phase angle of an input line, to AHM algorithm  510 . AHM algorithm  510  also receives input from AHM oversight controls  520  and field adjustable AHM parameters  540 . AHM algorithm  510  utilizes the inputs it receives to provide a signal configured to mitigate current or voltage harmonics input from the line and/or current or voltage harmonics output to the motor, provide phase current balance, and provide a desired amount of DC bus ripple. AHM algorithm  510  also outputs diagnostic information relating to the variable frequency drive and/or the overall system in which the drive is implemented. 
         [0021]    AHM oversight controls  520  may implement a number of AHM inhibit criteria which inhibit, turn off, or suspend AHM functionality, and a number of AHM diagnostic criteria which set a diagnostic fault code and/or reset the AHM algorithm or the system in which it is implemented. Certain embodiments utilize the criteria listed in Table 1 below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Error 
                 Inhibit 
                 Inhibit 
                 Diagnostic 
                 Diagnostic 
               
               
                 Condition 
                 Threshold 
                 Reset 
                 Threshold 
                 Reset 
               
               
                   
               
             
             
               
                 Frequency  
                 Frequency 
                 Frequency 
                 Frequency 
                 Frequency 
               
               
                 out of range 
                 &lt;47 Hz or 
                 returns to 
                 &lt;47 Hz or 
                 returns to 
               
               
                   
                 &gt;63 Hz for  
                 within 
                 &gt;63 Hz for  
                 within  
               
               
                   
                 any period  
                 47-63 Hz 
                 1 minute 
                 47-63 Hz 
               
               
                   
                 of time 
                   
                   
                   
               
               
                 Loss of  
                 No valid  
                 valid signal 
                 No valid  
                 valid signal 
               
               
                 AHM 
                 signal for N 
                 transitions 
                 signal 
                 transitions 
               
               
                 sync signal 
                 consecutive 
                   
                 transitions  
                   
               
               
                   
                 open  
                   
                 in open  
                   
               
               
                   
                 windows 
                   
                 portion of 
                   
               
               
                   
                   
                   
                 window 
                   
               
               
                   
                   
                   
                 function for  
                   
               
               
                   
                   
                   
                 1 minute 
                   
               
               
                 AHM sync 
                 Noise limit  
                 M contiguous 
                 &gt;60 seconds 
                 3 contiguous 
               
               
                 signal error 
                 of M  
                 bits in valid 
                 bit outside  
                 bits in valid 
               
               
                   
                 contiguous 
                 window 
                 of valid  
                 window 
               
               
                   
                 bits outside  
                   
                 window. 
                   
               
               
                   
                 of valid  
                   
                   
                   
               
               
                   
                 window 
                   
                   
                   
               
               
                 Excessive 
                 n/a 
                 n/a 
                 3 inhibits in 
                 DSP initialize 
               
               
                 AHM  
                   
                   
                 one minute  
                 or manual  
               
               
                 inhibit 
                   
                   
                 or 10 inhibits  
                 reset 
               
               
                   
                   
                   
                 in 1 hour 
               
               
                   
               
             
          
         
       
     
         [0022]    In Table 1 above, the frequency out of range condition may be determined with through evaluation of the line sync signal. The loss of AHM sync signal may occur over one cycle, one-half cycle, or other numbers of cycles or open windows. AHM sync signal errors may be determined based upon an evaluation of zero crossing events where a M zero crossing events, for example two zero crossing events, are expected per cycle and extra zero crossing events indicate an error state. The evaluation may include monitoring at time=½* 1/63 to ½* 1/47 and determining that unexpected zero crossing events have occurred within this time frame. 
         [0023]    Certain embodiments utilize additional or alternate criteria for AHM oversight controls  520 . Some embodiments criteria suspend, turn off or inhibit AHM functionality based upon the presence or detection of short term electrical disturbances, line voltage imbalance, incoming line frequency, and/or incoming line frequency rate of change. The short term electrical disturbances may include an electrical transient, a voltage surge, a ring wave, an electrical fast transient burst, an RF conducted immunity, a voltage variation, a voltage dip, a voltage interruption, and a voltage notch among others. 
         [0024]    Field adjustable AHM parameters  540  may include a number of calibratibles which may be utilized in controlling AHM functionality. Exemplary calibratibles include on/off enable/disable calibratibles, gain settings for current regulators and other routines or devices, current injection limits, and calibratibles specifying one or more harmonics to be targeted for mitigation, among others. 
         [0025]    AHM algorithm outputs  560  may include signals or commands configured to mitigate one or more input line harmonics such as input line harmonics and/or one or more output harmonics. Outputs  560  may also include signals or commands configured to enhance phase current balance and/or mitigate DC bus ripple. Outputs  560  further include diagnostics as to the state of the variable frequency drive such as those disclosed herein. Outputs  560  feed back to or influence inputs  550  in a closed loop fashion, though it shall be understood that open loop controls and diagnostics may also be utilized. 
         [0026]    It shall be understood that the exemplary embodiments summarized and described in detail above and illustrated in the figures are illustrative and not limiting or restrictive. Only the presently preferred embodiments have been shown and described and all changes and modifications that come within the scope of the invention are to be protected. It shall be appreciated that the embodiments and forms described below may be combined in certain instances and may be exclusive of one another in other instances. Likewise, it shall be appreciated that the embodiments and forms described below may or may not be combined with other aspects and features disclosed elsewhere herein. It should be understood that various features and aspects of the embodiments described above may not be necessary and embodiments lacking the same are also protected. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.