JP5399922B2 - System and method for extending the synchronous operation of an active converter in a variable speed drive - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This patent application claims the benefit of US Provisional Application No. 60 / 885,932, filed Jan. 22, 2007, and priority is claimed with respect to this provisional application.

  This application relates generally to variable speed drives. More specifically, this application relates to a system and method for synchronous operation of a variable speed drive having an active converter.

  A variable speed drive (VSD) for heating, ventilation, air conditioning and refrigeration (HVAC & R) applications typically includes a rectifier or converter, a DC link, and an inverter. Recent advances in drive technology have introduced the concept of active converters. The active converter gives the drive the ability to supply a sine wave input current to the power supply, and overcomes the problems associated with lower order harmonic currents that form lower order harmonic voltage distortions on the power distribution voltage. ease.

  VSD, which incorporates active converter technology to provide power factor correction and reduced input current harmonics, has a much higher level of common-mode voltage RMS and peak value for motor stator windings compared to conventional VSD. Also occurs. This common-mode voltage can be coupled to the motor rotor through various stray capacities of the device and cause fluting of the motor and compressor bearings, and these currents leading to current flowing through the device bearings. The common mode voltage can cause premature bearing failure in the motor and / or compressor.

  Proper operation of the active converter control technique using a synchronous dq reference frame requires information on the instantaneous phase angle of the input line voltage. If the angle of the reference frame is inaccurate or unknown, the input power factor and harmonic distortion of the input current to the variable speed drive (VSD) having the active converter cannot be controlled appropriately. If the VSD is required to ride through the increased loss of input line voltage and re-synchronize to the input power source when power is restored, maintain the expected dq reference frame angle during the power loss period A means to do is necessary. Furthermore, there is a need for a means for quickly recovering the lock on the line voltage of the input power source and generating the actual phase angle of the line voltage.

  There is a need for systems and / or methods that meet one or more of these needs or provide other advantageous features. Other features and advantages will be apparent from this specification. The disclosed teachings extend to embodiments that fall within the scope of the claims, regardless of whether they achieve one or more of the aforementioned needs.

  One embodiment relates to a variable speed drive system configured to receive an input AC voltage at a fixed AC input voltage and provide output AC power at a variable voltage and variable frequency. The variable speed drive includes a converter stage connected to an AC power source that supplies an input AC voltage, the converter stage configured to convert the input AC voltage to a boosted DC voltage, and the converter stage has a DC link And the DC link is configured to filter and store the boosted DC voltage from the converter stage, and the inverter stage is connected to the DC link, and the inverter stage is boosted from the DC link. The DC voltage is converted to output AC power having a variable voltage and a variable frequency. The variable speed drive includes a filter to prevent bearing erosion by common-mode and differential-mode filtering, and phase angle tracking to maintain information about the line voltage phase angle of the input AC power source under all conditions A system comprising two phase-locked loops (PPL) in a control scheme of an active converter, the two PLLs comprising a lead-lag filter with a relatively high filter cutoff frequency and a small value integrating capacitor An angular tracking system and a contactor bypass that operates at the highest frequency and voltage equal to the frequency of the power line power supplied to the VSD and eliminates losses associated with the VSD when the system needs to operate at the highest frequency. Integrated bypass actuated for VSD controlled systems Converter configuration, liquid or refrigerant cooled inductor, (1) film-based DC link capacitor, (2) a plurality of plastic coolers mounted on at least one power electronic module, (3) a plurality of active IGBT module of converter, (3) at least one stacked copper bus, (4) at least one gate driver control board, (5) at least one inverter gate resistance control board, and (6) at least one converter gate It also includes at least one of a power assembly comprising a resistance control board and a cooling module made of a plastic material capable of operating at a continuous use temperature of about 100 degrees Celsius.

Another embodiment relates to a method for extending the synchronous operation of an active converter to an AC power supply voltage during full line dropout.
Another embodiment relates to an active converter based variable speed drive system with improved maximum speed efficiency.

  Another embodiment relates to a liquid or refrigerant cooled inductor. Liquid or refrigerant cooled inductors may be used in any application where liquid or refrigerant cooling is available and where a reduction in the size and weight of the magnetic element is desired.

  A particular advantage of the embodiments described herein is that the integrated bypass active converter configuration is for a VSD controlled system where it operates at the highest frequency and voltage equal to the power line supply frequency supplied to the VSD. It can be used. Contactor bypass eliminates losses associated with VSD when the system needs to operate at the highest frequency.

  One advantage is that it reduces the common-mode voltage stress applied to the motor stator in both the RMS and peak terms, thereby reducing problems associated with premature failure of the bearings of the equipment and premature failure of the insulation to earth ground. May be relaxed. Another advantage is that it reduces the stress of the differential mode voltage applied to the motor stator in both the RMS and peak terms, thereby mitigating problems associated with premature failure between each winding of the device stator. Sometimes. Finally, this application addresses the problem of conducted EMI / RFI emissions associated with the operation of active converters.

  The present invention provides a compact, lightweight, easy-to-use and low-cost power assembly for (1) a film-based DC link capacitor, (2) a plastic cooler for power electronic modules, and (3) an active converter. It incorporates the elements of an IGBT module, (3) stacked copper busbars, (4) gate driver control board, (5) inverter gate resistance control board, and (6) converter gate resistance control board.

  Furthermore, variable speed drives incorporating active converter technology require the use of three phase inductors that are physically large, lossy and expensive compared to conventional passive converter based VSD designs. Another advantage of the disclosed invention is that by using induction core liquid cooling or refrigerant cooling, the size, weight and cost of the inductor required for an active converter based VSD is reduced. The inductor coil is also cooled by the core cooling means by heat conduction to the core.

Alternative exemplary embodiments relate to other features and combinations of features that may be generally recited in the claims.
The present application will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements, and in which:

1 is a schematic diagram of an overall system configuration. 1 is a schematic diagram of an overall system configuration. It is the schematic of embodiment of a variable speed drive device. It is the schematic of embodiment of a variable speed drive device. 1 is a schematic view of a refrigeration system. It is a block diagram of the angle maintenance control means of an active converter power supply.

  Before moving to the detailed illustration of an exemplary embodiment, it is to be understood that this application is not limited to the details or techniques set forth in the following description or illustrated in the figures. It should also be understood that the language and terminology used herein is for illustrative purposes only and should not be considered limiting.

  1A and 1B generally show the system configuration. The AC power supply 102 supplies power to a variable speed drive (VSD) 104, and the VSD 104 supplies power to one motor 106 (see FIG. 1A) or a plurality of motors 106 (see FIG. 1B). A motor 106 is preferably used to drive the corresponding compressor of the refrigeration system or cooling system (see generally FIG. 3). The AC power supply 102 supplies AC power having a fixed voltage and a fixed frequency in a single phase or multiple phases (for example, three phases) to the VSD 104 from an AC power transmission network or a local distribution system. The AC power supply 102 supplies an AC voltage or line voltage of 200V, 230V, 380V, 460V or 600V to the VSD 104, preferably at a line frequency of 50 Hz or 60 Hz depending on the corresponding AC power transmission network. it can.

  The VSD 104 receives AC power having a specific fixed line voltage and fixed line frequency from the AC power source 102, and at a desired voltage and desired frequency (both can be varied to meet specific requirements), AC power is supplied to 106. Preferably, the VSD 104 can supply AC power to the motor 106 having a voltage and frequency that is higher than the rated voltage and frequency of the motor 106 and a lower voltage and frequency. In another embodiment, the VSD 104 may supply a voltage that is less than or equal to the rated voltage of the motor 106 at a frequency that is higher and lower than the rated frequency of the motor 106. The motor 106 is preferably an induction motor, but can include any type of motor capable of operating at a variable speed. The induction motor can have any suitable pole arrangement including two poles, four poles or six poles.

  2A and 2B show another embodiment of the VSD 104. FIG. The VSD 104 may have three stages: a converter stage 202, a DC link stage 204 and an output stage with one inverter 206 (see FIG. 2A) or multiple inverters 206 (see FIG. 2B). Converter 202 converts AC power of a constant line voltage from AC power supply 102 to DC power at a constant line frequency. The DC link 204 filters the DC power from the converter 202 and provides an energy storage element. The DC link 204 can be composed of capacitors and coils, which are passive elements that exhibit high reliability and very low failure rates. Finally, in the embodiment of FIG. 2A, the inverter 206 converts the DC power from the DC link 204 to variable frequency, variable voltage AC power for the motor 106, and in the embodiment of FIG. Inverter 206 is connected in parallel, and each inverter 206 converts DC power from DC link 204 into AC power of variable frequency and variable voltage for the corresponding motor 106. Inverter 206 may be a power module that may include power transistors, insulated gate bipolar transistor (IGBT) power switches, and reverse diodes interconnected with wire bonding technology. Moreover, the DC link 204 and inverter 206 of the VSD 104 are different from those discussed above as long as the DC link 204 and inverter 206 of the VSD 104 can provide the appropriate output voltage and frequency to the motor 106. It should be understood that elements can be incorporated.

  1B and 2B, inverter 206 supplies AC power to the corresponding motor at the same desired voltage and desired frequency based on a common control signal or control command supplied to each inverter 206. In this way, it is controlled jointly by the control system. In another embodiment, the inverters 206 provide AC power at different desired voltages and frequencies to the corresponding motors 106 based on the individual control signals or control commands that each inverter 206 has supplied thereto. It is individually controlled by the control system so that it can be done. This capability allows the inverter 206 of the VSD 104 to more efficiently meet the demands and loads of the motor 106 and system regardless of the demands of other motors 106 and systems connected to the other inverters 206. For example, one inverter 206 can provide full output to the motor 106 while another inverter 206 supplies half of the power to another motor 106. In any embodiment, control of inverter 206 may be by a control panel or other suitable control device.

  There is a corresponding inverter 206 at the output stage of the VSD 104 for each motor 106 that will be powered by the VSD 104. The number of motors 106 that can be powered by the VSD 104 depends on the number of inverters 206 that are incorporated into the VSD 104. In one embodiment, there may be two or three inverters 206 connected in parallel with the DC link 204 and incorporated into the VSD 104 that is used to power the corresponding motor 106. The VSD 104 can have two to three inverters 206, but more than three inverters 206 are used as long as the DC link 204 can supply and maintain an appropriate DC voltage for each of the inverters 206. Please understand that you get.

  FIG. 3 generally illustrates one embodiment of the refrigeration or cooling system using the system configuration and VSD 104 of FIGS. 1A and 2A. As shown in FIG. 3, the HVAC, refrigeration system or liquid cooling system 300 includes a compressor 302, a condensing mechanism 304, a liquid cooling or evaporation mechanism 306, and a control panel 308. The compressor 302 is driven by a motor 106 that is powered by the VSD 104. The VSD 104 receives AC power having a constant line voltage and a constant line frequency from the AC power source 102, and at a desired voltage and desired frequency (both can be varied to meet specific requirements), the motor 106. To supply AC power. The control panel 308 can include a variety of separate elements such as an analog to digital (A / D) converter, a microprocessor, non-volatile memory, and an interface board to control the operation of the refrigeration system 300. A control panel 308 may also be used to control the operation of the VSD 104 and the motor 106.

  The compressor 302 compresses the refrigerant vapor and delivers the vapor to the condenser 304 through the discharge pipe. The compressor 302 may be any suitable type of compressor, such as a screw compressor, centrifugal compressor, reciprocating compressor, scroll compressor, and the like. The refrigerant vapor delivered to the condenser 304 by the compressor 302 enters a heat exchange relationship with a fluid (eg, air or water), and changes to a refrigerant liquid as a result of the heat exchange relationship with the fluid. Condensed liquid refrigerant from condenser 304 flows to evaporator 306 through an expansion device (not shown).

  The evaporator 306 may include a coupling for the supply line and the return line for the cooling load. A second liquid (eg, water, ethylene, calcium chloride brine, sodium chloride brine) proceeds to evaporator 306 via a return line and exits evaporator 306 via a supply line. The liquid refrigerant in the evaporator 306 enters a heat exchange relationship with the second liquid and lowers the temperature of the second liquid. The refrigerant liquid in the evaporator 306 changes to refrigerant vapor as a result of the heat exchange relationship with the second liquid. The vapor refrigerant in the evaporator 306 exits the evaporator 306 and returns to the compressor 302 by a suction pipe to complete the cycle. It should be understood that any suitable configuration of condenser 304 and evaporator 306 can be used in system 300 provided that appropriate phase changes of the refrigerant in condenser 304 and evaporator 306 are obtained.

  The HVAC, which is a refrigeration system or liquid cooling system 300, can include many other mechanisms not shown in FIG. These mechanisms have been deliberately omitted to simplify drawing for ease of illustration. Moreover, FIG. 3 shows the HVAC as a refrigeration system or liquid cooling system 300 with one compressor coupled with a single refrigerant circuit, but the system 300 is as shown in FIGS. 1B and 2B. It should be understood that a single VSD or multiple compressors powered by multiple VSDs can be included (shown in FIGS. 1A and 2A coupled to each of the one or more refrigerant circuits) See generally the embodiments).

  Referring now to FIG. 4, a power supply phase angle (MPA) control system, generally designated 900, is shown. The control system 900 provides retention of phase angle information regarding the AC input source or power supply voltage 102 during input voltage dropout. A power supply voltage 102 is applied to the squaring amplifier 901 to generate a substantially rectangular output signal from the AC input signal. The output of the squaring amplifier is input simultaneously to a pair of phase locked loops (PPL) 902 and 904. The first PLL 902 has a phase detector 918 for comparing the reference signal SIG with the comparison signal COMP in order to detect that the phase of the input signal is out of lock with the voltage controlled oscillator (VCO) 922. When the phase detector 918 detects that the two inputs SIG and COMP are out of phase lock, a reset signal is output from the terminal LD of the phase detector 918 to the one-shot circuit 924. The one-shot circuit 924 generates a narrow pulse input to the sample and hold (S & H) circuit 910. The output error signal of the phase detector 918 is passed to the VCO 922 through the delay advance filter circuit 906. Next, the output signal from the VCO 922 is input to the N frequency dividing circuit 926. The N divider circuit 926 provides a comparison signal applied to the COMP terminal of the phase detector 918 and also outputs a second signal indicating the dq axis digital angle output fast response 928 of the power supply voltage.

  The second PLL circuit 904 is configured in the same manner as the above-described PLL 902, and the phase detector 920 compares the input reference signal SIG with the comparison signal COMP and outputs an error signal to the delay advance filter 908. The delay advance filter 908 includes an S & H circuit 914 controlled by a one-shot circuit 930 and an analog switch 916. As described more fully below, the lag advance filter 908 has a low cutoff frequency. The VCO 932 is input to the N divider circuit 934. The N divider circuit 934 generates a comparison signal that is input to the COMP terminal of the phase detector 920, and generates a dq axis digital angle output low-speed response 936 of the power supply voltage. The second signal shown is also output.

  A control system 900 may be used to keep the VSD 104 synchronized, and the active converter 202 reduces current distortion and reapplies the AC input power supply voltage 102 to provide the VSD 104 with extended ride-through capability. At this time, energy regeneration is eliminated. With two PLLs 902, 904, the control system 900 can maximize the ability of the active converter 202 to maintain the best available information on the line voltage phase angle at the AC input source 102 under all conditions. It becomes possible. The delay advance filter 906 of the first PLL 902 has a relatively high filter cutoff frequency and a small value integrating capacitor C1. This filter 906 provides the active converter 202 with the capability for fast and accurate phase angle tracking under normal converter operating conditions. The elements of filter 906 include resistor R1, resistor R2, and capacitor C1. In one embodiment, the element values may be 43 kΩ for resistor R 1, 120 kΩ for resistor R 2, and 0.47 μF for capacitor C 1, but elements R 1, R 2, and C 1 of lag filter 906 are the desired cutoff frequency of filter 906 May be changed to adjust. The delay advance filter 908 of the second PLL 904 has a low cutoff frequency, a large value integration capacitor C2, and resistors R3 and R4. The lag advance filter 908 has the ability to store the power supply voltage angle in the PLL feedback loop during power shutdown due to the low cutoff frequency. In one embodiment, typical element values may be 510 kΩ for R3, 68 kΩ for R4, and 2.2 μF for C2. In order to improve the ability to maintain power phase angle information during power shutdown, each PLL feedback loop 906, 908 includes a sample and hold (S & H) circuit 910, 914, respectively, and includes an analog switch IC 912, 916, respectively. Including. The S & H circuits 910 and 914 having the analog switches 912 and 916 hold the accumulated charges on the integrating capacitors C1 and C2 in the delay advance filters 906 and 908, respectively, and the capacitor C1 due to leakage to the output terminal of the phase detector. , Prevents discharge of C2. The element sizing of the ratio R3 / R4 is also selected to minimize the step change in the voltage supplied to the voltage controlled oscillator 932 when the analog switch 916 switches.

  Switching of the analog switches 912 and 916 is controlled by detecting the total loss of the power supply voltage 102 via a power supply voltage detection (ie, power supply display) circuit. The sample and hold circuits 910 and 914 are controlled by an unlock detector incorporated in each phase detector. The VCO output is provided to n-divided bit counters 926, 934, where n is selected as a function of the phase angle resolution required for the particular application. These counter outputs are then fed back to a second input (denoted COMP) of each phase detector 918, 920 to form a closed loop. These counter outputs are also used to provide digital words 928, 936 representing the phase angle of the power supply. Digital words 928, 936 then manage the dq angle output during power shutdown. The selection of the timing for shifting the phase angle information is a function for a specific application, but normally a power supply voltage detection (power supply display) circuit is used. In one embodiment, PLLs 902, 904 may be implemented using a 74HC7046 IC manufactured by Phillips Semiconductor. The 74HC7046 IC includes a state machine type phase detector with an out of lock detector and a voltage controlled oscillator. This circuit design allows power interruption for up to 1 second without incurring a phase error of more than a predetermined angle under worst conditions.

  While the exemplary embodiments shown in the figures and described herein are presently preferred, it should be understood that these embodiments are provided merely as examples. Accordingly, this application is not limited to specific embodiments, but extends to various modifications that still fall within the scope of the appended claims. The order or sequence of any process or method steps may be varied or rearranged according to alternative embodiments.

  This application contemplates methods, systems, and program products on any machine-readable medium to accomplish its operations. Embodiments of the present application may be implemented using an existing computer processor, or by a dedicated computer processor for a suitable system incorporated for this or another purpose, or by a hardwire system. Good.

  It is important to note that the configuration and arrangement of the power supply phase angle control system shown in the various exemplary embodiments is merely exemplary. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art reviewing this disclosure will not substantially depart from the novel teachings and advantages of what is recited in the claims. , Easily understand that many variations are possible (eg changes in size, dimensions, structure, shape and size of various elements, parameter values, mounting mechanism, material application, color, orientation, etc.) Will do. For example, an element shown to be integrally formed may be composed of a plurality of parts or elements, the positions of the elements may be reversed or otherwise changed, and the nature of the individual elements Alternatively, the number or position may be changed or changed. Accordingly, all such modifications are intended to be included within the scope of this application. The order or sequence of any process or method steps may be varied or rearranged according to alternative embodiments. In the claims, the provisions of any means-plus-function are intended to cover not only the structures described to perform the functions listed herein but also the structural equivalents as well as equivalent configurations. Yes. Other substitutions, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of this application.

  As previously mentioned, embodiments within the scope of this application include a program product comprising a machine-readable medium for carrying or retaining stored machine-executable instructions or data structures. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other device with a processor. By way of example, such machine-readable media may be RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage device, magnetic disk storage device or other magnetic storage device, or any desired program code for executing the device. Any other medium that can be used to carry or hold in the form of instructions or data structures and that can be accessed by a general purpose or special purpose computer or other device having a processor can be provided. When information is communicated to or brought to the device over a network or another communication connection (hardwire, wireless, or a combination of hardwire and wireless), the device will properly view the connection as a machine-readable medium. Accordingly, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processor to perform a certain function or set of functions.

  It should be noted that although the figures herein may show a particular order of method steps, the order of these steps may be different from that shown. Also, two or more steps may be performed simultaneously or partially simultaneously. Such variations depend on the selected software and hardware system and the choice of the designer. It is understood that all such variations are within the scope of this application. Similarly, software implementations can be achieved with standard programming techniques with rule-based logic and other logic to accomplish various connection steps, processing steps, comparison steps and decision steps.

Claims (14)

A variable speed drive system configured to receive an input AC voltage at a fixed AC input voltage and supply output AC power at a variable voltage and variable frequency,
A converter stage connected to an AC power source for supplying the input AC voltage and configured to convert the input AC voltage into a boosted DC voltage;
A DC link connected to the converter stage and configured to filter and store the boosted DC voltage from the converter stage;
An inverter stage connected to the DC link and configured to convert the boosted DC voltage from the DC link to the output AC power having the variable voltage and the variable frequency;
A phase angle control circuit comprising a squaring amplifier, an associated first phase locked loop circuit and a second phase locked loop circuit;
The squaring amplifier is configured to receive the AC power and output a substantially rectangular output signal based on the AC power;
The first phase-locked loop circuit includes a first lag filter having a high filter cutoff frequency and a first capacitor configured to provide a phase angle parameter to the converter stage;
The second phase-locked loop circuit has a low cutoff frequency and a second capacitor to provide the ability to store the power supply voltage angle in the PLL feedback loop during power supply cutoff for the lag filter. A second lag advance filter configured as:
Variable speed drive system. The first delay advance filter includes a first resistor and a second resistor, the first resistor has a smaller resistance than the second resistor, and the first capacitor is the second capacitor. The variable speed driving device according to claim 1, wherein the variable speed driving device is an integrating capacitor having a value smaller than the value.   The resistance value of the first resistor is about 43 kΩ, the resistance value of the second resistor is about 120 kΩ, and the capacitance of the first capacitor is about 0.47 μF. The variable speed drive device described. The second delay advance filter includes a third resistor and a fourth resistor, the third resistor has a resistance greater than the fourth resistor, and the second capacitor is a resistance of the first capacitor. The variable speed drive device according to claim 3, wherein the variable speed drive device is an integral capacitor having a value larger than the value.   5. The resistance value of the third resistor is about 510 kΩ, the resistance value of the fourth resistor is about 68 kΩ, and the capacitance value of the second capacitor is about 2.2 μF. The variable speed drive device described in 1.   Each of the first phase-locked loop circuit and the second phase-locked loop circuit includes a first sample and hold circuit and a first analog switch in communication with the sample and hold circuit; Configured to retain charge stored on the associated first or second capacitor in the first or second lag advance filter and to prevent discharge of the associated first or second capacitor The variable speed drive apparatus according to claim 1.   A resistor that provides a resistance ratio between a third resistor and a fourth resistor that minimizes a step change in voltage supplied to the voltage controlled oscillator when the state of the second analog switch changes. The variable speed drive device according to claim 4, wherein the third resistor and the fourth resistor are selected based on the values.   Each of the first phase locked loop and the second phase locked loop further includes an analog switch and a power supply voltage detection circuit, and the power supply voltage detection circuit detects a loss of an input AC voltage of the AC power supply. The variable speed drive of claim 1, which is controlled. Each of the first phase-locked loop and the second phase-locked loop further includes a phase detection circuit, a voltage controlled oscillator, and an N divider circuit, and the phase detection circuit has a rectangular wave output of the squaring amplifier and 9. The variable speed drive of claim 8 , wherein the N divider counter has an out of lock detector responsive to a phase difference between comparison feedback signals generated in response to the voltage controlled oscillator. The variable speed driving device according to claim 9 , wherein the divisor n of the N divider counter is selected based on a desired resolution of the phase angle for a predetermined application. The divide-by-N counter generates a feedback signal by processing the output of the voltage controlled oscillator, the feedback signal to form a second given closed loop to the input terminal of each phase detector, according to claim 10 Variable speed drive. The N divider counter generates a digital word representative of the main phase angle, and the digital word is used to control the dq angle of the output of the variable speed drive during power supply voltage shutdown. Item 12. The variable speed drive device according to Item 11 . The variable speed driving device according to claim 12 , wherein the first phase locked loop circuit and the second phase locked loop circuit are configured to maintain a synchronous operation during a loss period of the AC power supply. The variable speed drive of claim 13 , wherein the loss period of the AC power supply is within 1 second, while the drive maintains a phase error within a predetermined angular limit.

Images