Pulse width modulation control module for inverter

Abstract

The invention discloses a pulse width modulation control module and system for an inverter. The system comprises an energy storage device; an inverter electrically coupled with the energy storage device; and a pulse width modulation module. The pulse width modulation module is configured to determine a modulation index according to the voltage of the energy storage device and the target output voltage of the inverter; selecting one of a plurality of pulse width modulation (PWM) methods according to the modulation index; and determining a switching instruction of the inverter according to the target output voltage and one of the selected PWM modulation methods.

Description

Technical Field

[0001] The present disclosure relates to a pulse width modulation control module for an inverter. Background Art

[0002] An electrical device such as a variable speed drive, adjustable speed drive, or uninterruptible power supply may be connected to an alternating current (AC) high power distribution system (e.g., an electrical grid). The electrical device drives, supplies power to, and / or controls a machine or non-machine type load. The electrical device may include an inverter that generates a drive signal for the load. Summary of the invention

[0003] In one aspect, the system includes: an energy storage device; an inverter electrically coupled to the energy storage device; and a pulse width modulation module. The pulse width modulation module is configured to: determine a modulation index according to a voltage of the energy storage device and a target output voltage of the inverter; select one of a plurality of pulse width modulation (PWM) methods according to the modulation index; and determine a switching instruction of the inverter according to the target output voltage and one of the selected plurality of PWM modulation methods.

[0004] Implementations may include one or more of the following features.

[0005] The plurality of PWM methods may include a near-state PWM method, a single-mode remote-state PWM method, and a dual-mode remote-state PWM method.

[0006] To select one of the plurality of PWM methods according to the modulation index, the pulse width modulation module may be configured to determine into which of the at least two modulation regions the modulation index falls.

[0007] The at least two modulation regions may include a remote state PWM region and a near state PWM region. The remote state PWM region may include: a single mode remote state PWM region and a dual mode remote state PWM region. Each region in the near state PWM region, the single mode remote state PWM region and the dual mode remote state PWM region may be defined by a corresponding minimum modulation index value and a maximum modulation index value. In these embodiments, the dual mode remote state PWM region is between the single mode remote region and the near state PWM region.

[0008] The system may further include an energy source electrically connected to the energy storage device, the energy source may be configured to provide a direct current (DC) current to the energy storage device. The energy source may be a rectifier.

[0009] The pulse width modulation module can be configured to select one of a plurality of PWM methods based on a modulation index and a setting, and the setting can indicate whether to reduce the common mode voltage. In some embodiments, if the setting indicates not to reduce the common mode voltage, one of the plurality of PWM methods selected is space vector pulse width modulation (SVPWM). The setting can be a value set according to a user input.

[0010] On the other hand, a control system for an inverter includes: a pulse width modulation module, which is configured to: determine a modulation index based on a voltage of an energy storage device in the inverter and a target output voltage of the inverter; select one of a plurality of pulse width modulation (PWM) methods based on the modulation index and one or more of the common mode voltage settings; determine a switching instruction of the inverter based on the target output voltage and one of the selected plurality of PWM modulation methods; and provide a switching instruction to the inverter, thereby modulating the DC energy in the energy storage device into a drive signal.

[0011] Implementations may include one or more of the following features.

[0012] The pulse width modulation module may be configured to select one of a plurality of PWM methods according to a modulation index and a common mode voltage setting. The common mode voltage setting may indicate whether to reduce the common mode voltage; and if the common mode voltage setting indicates that the common mode voltage is to be reduced, the pulse width modulation module may be configured to select one of a plurality of active voltage vector PWM methods according to the modulation index; if the common mode voltage setting indicates that the common mode voltage is not to be reduced, the pulse width modulation module may be configured to select space vector pulse width modulation (SVPWM). The plurality of active voltage vector PWM methods may include: a proximal state PWM method, a single mode remote state PWM method, and a dual mode remote state PWM method.

[0013] On the other hand, a method includes: determining a modulation index based on a voltage of an energy storage device in an inverter and a target output voltage of the inverter; selecting one of a plurality of pulse width modulation (PWM) methods based on the modulation index; determining a switching instruction of the inverter based on the target output voltage and one of the selected plurality of PWM modulation methods; and providing a switching instruction to the inverter, thereby controlling the inverter so as to modulate energy in the energy storage device into a drive signal provided to a load.

[0014] Implementations may include one or more of the following features.

[0015] Selecting one of the plurality of PWM methods according to the modulation index may include selecting one of a proximal state PWM method, a single mode remote state PWM method, a dual mode remote state PWM method, and a space vector pulse width modulation (SVPWM). In some embodiments, for a modulation index less than or equal to 0.906, a common mode voltage generated in the load by providing a drive signal to the load is less than a common mode voltage generated in the load by a drive signal generated by controlling an inverter based on a switching command determined according to a target output voltage and a standard SVPWM. In some embodiments, for a modulation index less than or equal to 0.906, a common mode current generated in the load by providing a drive signal to the load is less than a common mode current generated in the load by a drive signal generated by controlling an inverter based on a switching command determined according to a target output voltage and a standard SVPWM.

[0016] Selecting one of the plurality of PWM methods may include selecting a PWM method having a linear region including a determined modulation index.

[0017] Embodiments of any technology described herein may include devices, apparatus, systems, control systems, machine executable instructions, and / or methods. Details of one or more embodiments are described in detail in the accompanying drawings and the following specification. Other features will be apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is an example of a system including an inverter.

[0019] Figure 2 is another example of a system including an inverter.

[0020] Figure 3 is a block diagram of an example control scheme.

[0021] Figure 4 is a diagram including the inverter voltage vector.

[0022] Figure 5 An example of inverter switching command is shown.

[0023] Figure 6 is a flow chart of an example of a common-mode voltage reduction process.

[0024] Figure 7 A-7C and 8A-8C show simulated data. DETAILED DESCRIPTION

[0025] Figure 1System 100 is shown. System 100 includes electrical device 110, which includes DC power supply 117, energy storage device 118 and inverter 119. DC power supply 117 provides DC current (Idc) to energy storage device 118. DC power supply 117 can be, for example, a battery or a generator. In some embodiments (e.g. Figure 2 As shown), the power supply 117 is a rectifier, which converts the AC current into a DC current Idc. Figure 1 In the example of , the energy storage device 118 includes capacitors C1 and C2 connected to the ground midpoint (labeled as o). The DC current Idc flows into the energy storage device 118 and is stored as potential energy. The inverter 119 modulates the energy stored in the energy storage device 118 into a three-phase drive signal 104 provided to the AC motor 102. The three-phase drive signal 104 is an alternating current (AC) or a time-varying voltage signal, and the characteristics (amplitude, frequency and / or phase) of the three-phase drive signal 104 control the speed, direction and torque of the motor 102.

[0026] The inverter 119 includes controllable switches SW1 to SW6. Each controllable switch SW1 to SW6 is any type of electronic switch with a controllable state. The switches SW1 to SW6 can be controlled to a specific state (e.g., on or off). In the example shown, each switch SW1 to SW6 is a transistor, and the state of each switch SW1 and SW6 can be controlled by adjusting the gate voltage of the transistor.

[0027] The motor 102 is a three-phase AC motor, such as, for example, an induction motor or a permanent magnet synchronous motor. The motor 102 includes a spatially fixed stator 109 and a rotor (not shown) that rotates relative to the stator 109 when a drive signal 104 is applied. Each phase of the stator 109 includes an electrical winding: 109a, 109b, and 109c. The winding 109a is electrically connected to switches SW1 and SW4, the winding 109b is electrically connected to switches SW2 and SW6, and the winding 109c is electrically connected to switches SW5 and SW2. The motor 102 also includes a frame 108. During operational use of the system 100, the frame 108 is typically grounded.

[0028] The system 100 also includes a control system 130 that generates switching instructions 151. When provided to the inverter 119, the switching instructions 151 operate the controllable switches SW1 to SW6 in a switching pattern defined by the switching instructions 151 to produce a target or reference inverter output voltage (Vref). In any given switching pattern, the switches of each phase leg are complementary and have opposite states. In other words, if the switching instructions 151 command SW1 to be in the off state, then SW4 is commanded to be in the on state.

[0029] Space vector pulse width modulation (SVPWM) is a common method for generating switching commands 151. However, using control signals generated based on standard SVPWM to control an inverter that drives an AC motor may generate a considerable common mode voltage (CMV) in the AC motor. CMV is measured from ground or the DC bus midpoint ( Figure 1 The average value of the three-phase voltage potential (Vao, Vbo, Vco) with the point marked as o in the figure as the reference. Voltage Vao is the voltage of the point marked as (a) relative to the ground; voltage Vbo is the voltage of the point marked as (b) relative to the ground; voltage Vco is the voltage of the point marked as (c) relative to the ground.

[0030] CMV may present challenges such as electromagnetic interference and excessive bearing currents. In addition, the amplitude fluctuations of CMV tend to generate common-mode currents, which flow to ground through the parasitic capacitance between the windings 109a, 109b, 109c and the frame 108. The parasitic capacitance between the windings 109a, 109b, 109c and the stator iron, the parasitic capacitance between the windings 109a, 109b, 109c and the rotor iron, the capacitance between the rotor iron and the stator iron, and / or the ball bearings in the motor 102 may provide additional flow paths for the common-mode current. The amplitude of the common-mode current depends on the fluctuation rate of the CMV, which increases with the switching frequency of the controllable switches SW1 to SW6. Common-mode currents may increase electromagnetic interference (EMI) and cause premature failure of the ball bearings and / or other components of the motor 102. The presence of electromagnetic interference may cause noise in the motor and / or make the electrical device 210 more likely to fail to meet electromagnetic compatibility standards.

[0031] One reason that standard SVPWM may produce relatively high CMV is that standard SVPWM utilizes a zero voltage vector as part of the switching pattern that commands the inverter 119. The zero voltage vector represents a state in which SW1, SW3, SW5 are simultaneously off (or on), while the complementary switches SW4, SW6, SW2 are simultaneously on (or off). Some conventional methods attempt to reduce CMV by eliminating the zero voltage vector in the inverter switching pattern, but these methods may have drawbacks. For example, within a relatively narrow operating range of the inverter 119, these methods may produce lower or acceptable harmonic distortion and lower or acceptable CMV.

[0032] In another aspect, the control system 130 includes a pulse width modulation (PWM) module 180 that employs a multi-faceted approach involving more than one PWM-based modulation technique to reduce CMV in the motor 102. This multi-faceted approach reduces CMV over the entire operating range of the inverter 119. As described in detail below, the PWM module 180 generates the switching commands 151 based on one of a plurality of pulse width modulation (PWM)-based techniques. Compared to an approach that uses only standard SVPWM modulation, the PWM module 180 reduces CMV while maintaining voltage linearity over a wide output voltage and frequency range of the inverter 119.

[0033] Figure 2 2 is a schematic diagram of a system 200. The system 200 includes an electrical device 210, which includes a rectifier 217, a DC link 218, and an inverter 219. The inverter 219 provides a three-phase drive signal 204 for the motor 202. The control system 230 includes a PWM module 380 that generates a switching command 251. The switching command 251 controls the inverter 219 to generate the three-phase drive signal 204. The switching command 251 operates the controllable switches SW1 to SW6 in a specific pattern to generate a target or reference inverter output voltage.

[0034] Before discussing the control scheme 306 and the PWM module 380 in more detail, an overview of the system 200 is provided.

[0035] exist Figure 2 In the example of FIG. 2 , the load 202 is a three-phase motor 202, such as an induction motor or a permanent magnet synchronous motor, for example. The motor 202 includes a spatially fixed stator 209 and a rotor 208 that rotates relative to the stator 209 when a drive signal 204 is applied. Each phase of the stator 209 includes an electrical winding: 209a, 209b, and 209c. The motor 202 includes a motor similar to Figure 1 The frame of the frame 108 is shown. Loads other than motors may be used in the system 200.

[0036] The power distribution network 201 distributes AC power with a base frequency of, for example, 50 or 60 Hertz (Hz). The operating voltage of the distribution network 201 can be up to 690 V. For example, the distribution network 201 may include, for example, one or more transmission lines, distribution lines, cables and / or any other power transmission mechanism. The distribution network 201 includes three phases, referred to as a, b and c.

[0037] The electrical device 210 comprises input nodes 214a, 214b, 214c, each node being electrically coupled to a respective one of the three phases a, b, c of the distribution network 201 through a respective filtering system 216a, 216b, 216c. Each filtering system 216a, 216b, 216c may be an inductor.

[0038] The electrical device 210 includes a rectifier 217, a DC link 218, and an inverter 219. The rectifier 217 is a three-phase six-pulse bridge including six electronic switches. Figure 2 In the example of FIG. 1 , the six electronic switches are diodes D1-D6. Each diode D1-D6 includes a cathode and an anode and is associated with a forward bias voltage. When the anode voltage is greater than the cathode voltage by at least the bias voltage, each diode D1-D6 allows current to flow in the forward direction (from the anode to the cathode). When the voltage difference between the anode and the cathode is less than the forward bias voltage, the diode does not conduct current in the forward direction.

[0039] Input node 214a is electrically connected to the anode of diode D1 and the cathode of diode D4. Input node 214b is electrically connected to the anode of diode D3 and the cathode of diode D6. Input node 214c is electrically connected to the anode of diode D5 and the cathode of diode D2. Diodes D1-D6 rectify input currents ia, ib, ic into direct currents id.

[0040] The diodes D1-D6 are also electrically connected to the DC link 218. The cathode of each diode D1, D3, D5 is electrically connected to the DC link 218, and the anode of each diode D2, D4, D6 is electrically connected to the DC link 218. The DC link 218 includes a capacitor network C. The rectified current id flows into the capacitor network C and is stored. The capacitor network C includes one or more capacitors, and when the rectified current id flows in from the rectifier 217, the capacitor stores electric energy; when the rectified current id does not flow in from the rectifier 217, the capacitor releases the stored electric energy.

[0041] The inverter 219 converts the DC power stored in the capacitor network C into a three-phase AC drive signal 204 provided to the load 202. The inverter 219 includes a network of electronic switches SW1-SW6, which are controlled by the control system 230 to generate the drive signal 204. For example, each switch SW1-SW6 can be a power transistor. The three-phase drive signal 204 has phase components 204u, 204v, 204w, each of which is provided to one of the three phases of the load 202.

[0042] The system 200 also includes a sensor system 238 for measuring and / or estimating properties or parameters of the drive signal 204 and / or the motor 202. For example, the sensor system 238 may include a current sensor that measures the amount of current drawn in each phase of the motor 202 and / or a voltage sensor that measures the voltage of each phase component 204u, 204v, 204w of the drive signal 204. The sensor system 238 may also include a sensor that measures the angular position of the rotor 208 of the motor 202 and / or the angular velocity of the rotor 208. In some embodiments, the control system 230 uses data from the sensor system 238 (except for directly measured position data) to estimate the angular position and / or angular velocity of the rotor 208 according to sensorless techniques.

[0043] The control system 230 generates switching instructions 251 that control the switching pattern of the switches SW1-SW6 to generate a drive signal 204 having specific characteristics (e.g., amplitude, frequency, and / or phase). The control system 230 implements a control scheme 306 including a PWM module 380, both of which refer to Figure 3 discuss.

[0044] Control system 230 includes electronic processing module 232, electronic memory 234, and input / output (I / O) interface 236. Electronic processing module 232 includes one or more electronic processors. The electronic processor of module 232 can be any type of electronic processor and may or may not include a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a field programmable gate array (FPGA), a complex programmable logic device (CPLD), and / or an application specific integrated circuit (ASIC).

[0045] Electronic storage 234 may be any type of electronic storage capable of storing data and instructions in the form of a computer program or software, and electronic storage 234 may include volatile and / or non-volatile components. Electronic storage 234 and processing module 232 are coupled so that processing module 232 can access or read data from electronic storage 234 and write data to electronic storage 234. The instructions stored in electronic storage 234, when executed, cause electronic processing module 232 to analyze data and / or retrieve information. Electronic storage 234 may also store information about system 200. For example, electronic storage 234 may store information about motor 202 or inverter 219.

[0046] In addition, the electronic storage 234 can also store executable instructions that implement the control scheme 306 and the PWM module 380. The executable instructions can include software, subroutines, modules and / or functions that implement standard SVPWM, near-state PWM, far-state PWM, single-mode far-state PWM, and dual-mode PWM. These different PWM methods will be discussed below. The electronic storage 234 can also store data and / or information for the control scheme 306 and / or the PWM module 380. For example, the electronic storage 234 can store thresholds and / or boundary values ​​associated with the operating mode of the inverter 219 and a variety of PWM-based methods.

[0047] The I / O interface 236 may be any interface that allows a human operator and / or an autonomous process to interact with the control system 230. For example, the I / O interface 236 may include, for example, a display (e.g., a liquid crystal display (LCD)), a keyboard, audio input and / or output (e.g., a speaker and / or a microphone), a visual output in addition to or in lieu of a display (e.g., a light, a light emitting diode (LED)), a serial or parallel port, a universal serial bus (USB) connection, and / or any type of network interface, such as, for example, Ethernet. The I / O interface 236 may also communicate without physical contact by means of, for example, IEEE 802.11, Bluetooth, or near field communication (NFC) connections. For example, the control system 230 may be operated, configured, modified, or updated through the I / O interface 236.

[0048] The I / O interface 236 also allows the control system 230 to communicate with components in the system 200 and remote systems external to the system 200. For example, the I / O interface 236 can control a switch or switch network (not shown) or circuit breaker within the system 200 to allow the electrical device 210 to be disconnected from the distribution network 201. In another example, the I / O interface 236 can include a communication interface that allows communication between the control system 230 and a remote station (not shown) or between the control system 230 and a separate monitoring device. The remote station or monitoring device can be any type of station through which an operator can communicate with the control system 230 without having physical contact with the control system 230. For example, the remote station can be a computer-based workstation, a smart phone, a tablet, or a laptop computer connected to the control system 230 through a service protocol, or a remote control connected to the control system 230 through a radio frequency signal.

[0049] Other embodiments of the electrical device 210 are possible. For example, the rectifier 217 may be a diode-thyristor hybrid rectifier, or an active front end including six transistors or other controllable switches instead of diodes D1-D6. The electrical device 210 may be an adjustable speed drive, a variable frequency drive, or a variable speed drive.

[0050] Figure 3 3 is a block diagram of the control scheme 306. The control scheme 306 includes a PWM module 380 that generates a switching command 251 to control switches S1 to S6 of the inverter 219. The inverter 219 generates a three-phase drive signal 204 under the control of the switching command 251.

[0051] The control scheme 306 includes a comparator 359 for comparing the target angular velocity (ω*) of the motor 202 and the observed angular velocity (ωo) of the rotor 208 and providing the difference (Δω) to the speed controller 352. The observed angular velocity (ωo) is determined by providing a measured or estimated angular position (θo) of the rotor 208 to the derivative block 358. The observed angular position (θo) of the rotor 208 is output by the angular position block 367, which determines the observed angular position (θo) by a position sensor in the sensor system 238 or by using a sensorless angular position estimation technique. The derivative block 358 determines the observed angular velocity (ωo) by calculating the rate of change of the angular position (θo) over a period of time.

[0052] The sensor system 238 also measures the current drawn by each phase of the motor 202 (each stator winding 209a, 209b, 209c). The measured currents are ia, ib and ic respectively. The measured currents ia, ib, ic are provided to the modulation block 356, which implements the Clarke transformation to convert the three-phase current (ia, ib, ic) into two orthogonal current components: the component iα along the α axis and the component iβ along the β axis (orthogonal to the α axis). The Clarke transformation projects the three-phase quantity (such as the current flowing through the windings 209a, 209b, 209c of the stator 209 or the voltage applied to the windings 209a, 209b, 209c of the stator 209) onto a two-dimensional stationary coordinate system defined by the α axis and the β axis. The Clarke transformation is shown in formula (1):

[0053] Formula (1),

[0054] Where, ia, ib, ic are the instantaneous currents in the stator windings 209a, 209b, 209c, i αβ is a vector including a component along the α axis (365) and a component along the β axis (366). Vectors 365 and 366 are provided to a modulation block 364 which performs a Park transform. The Park transform rotates the stationary α, β axes by a frequency ω.

[0055] The Park transform is shown in formula (2):

[0056] Formula (2),

[0057] Among them, i dqis a vector including a component along the d-axis (ido, or observed d-axis current) and a component along the q-axis (iqo, or observed q-axis current); θ is the observed angular position (θo) of the rotor 208 of the motor 202 .

[0058] The speed controller 352 generates a torque command Te* and provides it to the current command generator block 353. The current command generator block 353 generates a d-axis current command id* and a q-axis current command iq*. The comparator 357 compares the d-axis current command id* with the observed d-axis current (ido) to determine the difference (Δid) between id* and ido*, and provides the difference (Δid) to the d-axis current controller 354d. The comparator 361 compares the q-axis current command iq* with the observed q-axis current (iqo) to determine the difference (Δiq) between iq* and iqo, and provides the difference (Δiq) to the q-axis current controller 354q.

[0059] The d-axis current controller 354d is a proportional-integral (PI) controller having a predetermined gain constant Kd. The q-axis current controller 354q is a PI controller having a predetermined gain constant Kq. The d-axis current controller 354d determines a d-axis voltage command ud* that minimizes the d-axis current error (Δid). The q-axis current controller 354q determines a q-axis voltage command uq* that minimizes the q-axis current error (Δiq).

[0060] The d-axis voltage command ud* and the q-axis voltage command uq* are provided to the modulation block 355, which implements the inverse Park transform. The inverse Park transform projects the d-axis and q-axis voltage commands (ud*, uq*) onto the stationary α, β reference frame. The outputs of the modulation block 355 are uα* and uβ*, which are the components of the voltage applied to the stator 209 in the stationary α, β reference frame.

[0061] The voltage commands uα* and uβ* are provided to the PWM module 380 . The module 380 implements PWM-based control to generate the switching commands 251 .

[0062] As described above, the inverter 219 includes controllable switches S1 to S6, each of which can be controlled to be in an on state or an off state. For example, each switch S1 and S6 can be turned on or off by controlling the voltage of the switch gate. When applied to the inverter 219, the switch instruction 251 operates the switches S1 and S6 in a specified switching mode by controlling the voltage of each switch gate. For example, the switch instruction 251 can control a voltage source and / or a current source (not shown) to control the gate voltage.

[0063] The states of switches S1 to S6 are controlled and change over time in a switching pattern defined by switch instructions 251. Switches S1, S3 and S5 are upper switches, and switches S4, S6 and S2 are lower switches. There are eight valid switch configurations or state combinations for switches S1, S3 and S5. The switch states are represented by space vectors (also called voltage vectors) V1 to V8. The switch states V1 to V8 of the upper switches S1, S3 and S5 are shown in Table 1:

[0064] Vector S1 S3 S5 V1 1 0 0 V2 1 1 0 V3 0 1 0 V4 0 1 1 V5 0 0 1 V6 1 0 1 V7 0 0 0 V8 1 1 1

[0065] The state of each lower switch S4 , S6 , S2 is opposite to the state of the corresponding upper switch S1 , S3 , S5 , so the inverter 219 has a total of eight switch configurations or combinations.

[0066] See also Figure 4 , six non-zero (or active) vectors (V1 to V6) define a hexagon 439 and six sectors (1 to 6) in a rectangular coordinate system (Re, Im). The angle between any two adjacent non-zero vectors (V1 to V6) is 60 degrees (°). Two zero vectors (V7 and V8) are located at the origin. The perimeter of the hexagon 439 represents the operating limit of the inverter 219.

[0067] The voltage commands uα* and uβ* input to the PWM module 380 are Figure 4 The vector Vref is defined by the phase angle (θref) in the Re, Im coordinate system shown. The voltage vector (Vref) and the angle (θref) are called the target or reference voltage and the target or reference angle, respectively. The modulation index (M) associated with the target or reference voltage is determined by equation (3):

[0068] Formula (3),

[0069] Where M is the modulation index, Vref is the amplitude of the reference voltage or target voltage, and Vdc is the measured voltage across the DC link 218. The modulation index has a value between 0 and 1.

[0070] PWM module 380 uses the modulation index (M) and / or CMV reduction flag to determine which of multiple PWM based methods to use to synthesize Vref and generate switching commands 251. Multiple PWM based methods include near state PWM method, single mode remote state PWM method, dual mode remote state PWM method and standard SVPWM.

[0071] In standard SVPWM, the switch states V1 through V8 are combined into voltage vectors of arbitrary magnitude and angle within the approximate hexagon 439. For example, a desired inverter output voltage having a magnitude represented by the vector Vref and a phase angle θref that places the voltage vector in sector 1 is achieved by a switching sequence that uses two adjacent switch states (V1 and V2 in this example) for a specified period of time and a zero vector (V7 or V8) for the rest of the time.

[0072] In the near-state PWM method, Vref is composed of three non-zero (or active) voltage vectors: the voltage reference closest to Vref is the first voltage vector, and the two voltage vectors adjacent to the first voltage vector are the second and third voltage vectors. Figure 4 In the example shown, Vref is closest to the voltage vector V1. According to the near-state PWM method, the three voltage vectors used to synthesize Vref will be V1, V2 and V6. Continuing with this example, Vref is synthesized as shown in formula (4):

[0073] Formula (4),

[0074] Where Ts is the time of a section or switching cycle of the switching command 252; T1, T2 and T6 are dwell times. For Vref in sector 1, the dwell time of the near-state PWM method is determined as follows:

[0075] Formula (5a),

[0076] Formula (5b),

[0077] as well as Formula (5bc),

[0078] Where Ts is the switching cycle time, M is the modulation index of the reference or target voltage Vref, and θ is θref.

[0079] The switch command 251 is a binary signal that switches between a high level (1) and a low level (0) within a switching period Ts and is symmetrical about the midpoint of the switching period. The dwell time determines how long the switch command 251 remains high or low under a specific voltage vector. Figure 5 An example of the switching command 251 within one switching cycle Ts determined according to equations (4) and (5a) to (5c) is shown.

[0080] In the remote state PWM method, Vref in sector 1 (e.g. Figure 4 The dwell time of the

[0081] Formula (6a),

[0082] Formula (6b),

[0083] Formula (6c),

[0084] as well as Formula (6d),

[0085] Where Ts is the switching cycle time, M is the modulation index of the target or reference voltage Vref, and θ is θref.

[0086] In single mode remote state PWM, Vref is synthesized by active (non-zero) voltage vectors that are 120° apart from each other. In other words, single mode remote state PWM synthesizes Vref using only odd non-zero voltage vectors (V1, V3, V5) or only even non-zero voltage vectors (V2, V4, V6). Therefore, switching command 251 includes only odd non-zero voltage vectors or only even non-zero voltage vectors.

[0087] In dual-mode remote state PWM, sectors 1 to 6 and non-zero voltage vectors V1 to V6 are connected to Figure 4 The sectors shown are rotated 30° clockwise compared. In dual mode remote state PWM, non-zero voltage vectors V1 to V6 define the sectors of rotation as follows: Sector 1: 330°≤θref<30°, Sector 2: 30°≤θref<90°, Sector 3: 90°≤θref<150°, Sector 4: 150°≤θref<210°, Sector 5: 210°≤θref<270°, Sector 6: 270°≤θref<330°. If the reference voltage Vref is in sectors 1, 3, or 5 of rotation, only odd voltage vectors (V1, V3, V5) are used to synthesize Vref. If Vref is in sectors 2, 4, or 6 of rotation, only even voltage vectors (V2, V4, V6) are used to synthesize Vref.

[0088] In the linear operating region of each non-zero voltage vector PWM based method, the dwell time equations (Equations (5a) to (5c) and (6a) to (6d)) produce meaningful results and the inverter 219 acts as a linear voltage amplifier. Outside the linear operating region of a particular active voltage vector PWM based method, generating switching commands 251 using this method causes the inverter 219 to no longer act as a linear amplifier, increasing the common mode voltage in the motor 202 and generating low frequency harmonics at the output of the inverter 219 that distort the current in the motor coils 209a, 209b, 209c.

[0089] The linear operating region of each active voltage vector PWM method is defined by a range of modulation index (M). The linear operating region of the single-mode remote PWM method includes modulation index (M) less than or equal to 0.524. The linear operating region of the dual-mode remote PWM method includes modulation index (M) greater than 0.524 and less than or equal to 0.605. The linear operating region of the near-state PWM method includes modulation index (M) greater than 0.605 and less than 0.906.

[0090] Figure 4 The linear operating region of the method based on active vector PWM is shown. A first circle 441 with a radius of 0.906 is inscribed in the hexagon 439, a second circle 443 with a radius of 0.605 is located within the first circle 441, and a third circle 445 with a radius of 0.524 is located within the second circle 443. The third circle 445 defines a single-mode remote state linear operating region 446. A reference voltage (Vref) with a modulation index (M) falling within the range of the third circle 445 can be synthesized using a single-mode remote state PWM method while maintaining the voltage linearity of the inverter 219. A ring 447 between the third circle 445 and the second circle 443 defines a dual-mode remote state operating region 447. A reference voltage (Vref) with a modulation index (M) in region 447 can be synthesized using a dual-mode remote state PWM method while maintaining the voltage linearity of the inverter 219. A ring 448 between the second circle 443 and the first circle 441 defines a near-end state linear operating region. A reference voltage (Vref) having a modulation index (M) within the loop 448 may be synthesized using a near-state PWM method while maintaining the voltage linearity of the inverter 219.

[0091] See also Figure 6 , a flow chart of process 600 is shown. Process 600 is an example of a common mode voltage reduction process that can be implemented by control system 230 and PWM module 380. Process 600 can be implemented as executable instructions stored on electronic memory 234 and executed by electronic processing module 232. Process 600 can be implemented as software and can be programmed into the control system of an existing power converter. In addition, process 600 can also be implemented as a control system or controller that is installed in an existing power converter as a software update or as part of a firmware update.

[0092] The modulation index (M) is determined (610) using equation (3). In equation (3), the voltage of the DC link 218 (VDC) is the measured value of the voltage across the DC link 218, and Vref is the voltage of the modulation block 355 ( Figure 3 ) is the reference voltage related to the voltage command (uα*, uβ*) output.

[0093] The process 600 determines whether to reduce the common mode voltage (CMV) (612). The determination of whether to reduce the CMV may include analyzing a flag or a user input. For example, an operator of the power converter 210 may indicate that the PWM module 380 should be activated by, for example, selecting a CMV reduction mode at the I / O interface 236. In these embodiments, the input sets the value of a flag stored on the electronic memory 234 to reflect the operator's selection. For example, if the operator turns on the CMV reduction mode, the flag is set to 1. If the operator turns off the CMV reduction mode, the flag is set to 0. In these embodiments, if the flag is 1, the PWM module 380 is activated; if the flag is 0, the PWM module 380 is not activated. An entity other than the operator may select the CMV reduction mode through the I / O interface 236. For example, a manufacturer of the power converter 210 may select or deselect the CMV reduction mode through the I / O interface 236, or hard-code the flag value before providing the inverter 219 to the end user.

[0094] In some embodiments, the value of the flag is set to 1 or 0 by an entity other than the operator, such as a manufacturer, distributor, or assembler of power converter 210. In these embodiments, if the flag is set to 1, PWM module 380 is always activated.

[0095] If CMV reduction is not indicated, the switching command 251 is determined according to the standard SVPWM method (645). If CMV reduction is indicated, the modulation index (M) determined in (610) is compared with the linear operating boundary of the remote state PWM method to determine whether the modulation index (M) is in the linear operating region of the single mode remote state PWM method or the dual mode remote state PWM method (615). Less than or equal to 0.605 ( Figure 4 The modulation index (M) of the remote state PWM method (the radius of the second circle 443 in (610)) is within the linear operating region of one of the two remote state PWM methods. Therefore, in order to determine whether the modulation index (M) determined in (610) is within the linear operating region of the remote state PWM method, the modulation index (M) is compared with 0.605. If the modulation index (M) is greater than 0.605, the modulation index (M) is not within the linear region of the remote state PWM method, and the process proceeds to (635). If the modulation index (M) is on or inside the second circle 443 (which would be the case if M is less than or equal to 0.605), one of the remote state PWM methods can be used to synthesize the reference voltage Vref while maintaining the voltage linearity of the inverter 219. The process proceeds to (620) to determine which of the two remote state PWM methods to select.

[0096] At (620), the modulation index (M) determined in (610) is compared to the boundary defining the single mode remote state PWM method. The boundary defining the single mode remote state PWM method is the third circle 445 ( Figure 4 ). Therefore, if the modulation index (M) is less than or equal to the radius (0.524) of the third circle 445, and the reference voltage Vref is located within or on the third circle 445, the single mode remote state PWM method is selected. The switching command 251 is determined using the single mode remote state PWM method (625).

[0097] Returning to (620), if the modulation index (M) is greater than 0.524 but less than or equal to 0.605, the modulation index (M) is not in the single mode remote state linear operating region 446, but is in the dual mode remote state PWM linear operating region 447. The dual mode remote state PWM method is selected. The switching command 251 is determined using the dual mode remote state PWM method (630).

[0098] Returning to (615), if the modulation index (M) determined in (610) is not within the far-state linear region, process 600 determines whether the modulation index (M) is within the near-state PWM linear operating region 448 (635). If the modulation index (M) is greater than 0.605 and less than or equal to 0.906, then the modulation index (M) is within the near-state PWM linear region 448. Switching commands 251 are determined using the near-state PWM method (640).

[0099] If the modulation index (M) determined in (610) is not within the near-state PWM linear region 448, then none of the three active voltage vector PWM methods are selected and the switching commands 251 are determined using standard SVPWM (645).

[0100] The switching command 251 is provided to the inverter 219 to generate a reference voltage or a target voltage (Vref) at the output of the inverter 219 .

[0101] There may be other implementations of process 600. For example, in some implementations, the modulation index (M) is determined only when there is an indication that CMV reduction is to be performed. In other words, (612) may be performed before (610). In these implementations, when CMV reduction is not performed, process 600 proceeds to (645) to determine the switching command 251 according to the standard SVPWM without determining the modulation index (M) associated with the target voltage or reference voltage Vref.

[0102] Figure 7A-7C and 8A-C relate to simulation results. The simulated system is similar to system 100. In the simulation, Vdc is 300 volts (V), and the inverter supplies power to a three-phase RL load having a resistance (R) of 10 ohms (Ω) and an inductance (L) of 6.5 millihenries. The inverter generates a three-phase drive signal after receiving a switching command from the control system.

[0103] Figure 7 B and 7C show the results when the control system does not include the PWM module 380 and the switching commands are generated by standard SVPWM only. Figure 8 8B and 8C show that the control system includes the PWM module 380 and the switching commands are simulation results generated by the PWM method using the process 600 discussed above.

[0104] Figure 7 A and 8A show the commanded motor speed (in Hz) as a function of time (in seconds). Figure 7 B and 8B show the common mode voltage induced in the motor as a function of time (seconds). Figure 7 C and 8C show the three-phase motor current as a function of time (seconds). Standard SVPWM simulation ( Figure 7 B and 7C) and the analog of the PWM module 380 ( Figure 8 B and 8C) command motor speed ( Figure 7 A and 8A) are the same. Figure 7 The time scale is the same for all graphs in A-7C and 8A-8C.

[0105] like Figure 7 As shown in B, in the standard SVPWM method, the amplitude of the common mode voltage is about + / -150V. Figure 8 B, PWM module 380 significantly reduces the common mode voltage. When the motor speed is below about 48 Hz, the common mode voltage is substantially eliminated. For motor speeds above about 48 Hz, the amplitude of the common mode voltage is only one-third of the common mode voltage of the standard SVPWM (the amplitude is between about + / - 50V). Therefore, PWM module 380 greatly reduces the amount of common mode voltage induced in the motor.

[0106] Figure 7 C shows the current drawn by the RL load when using the standard SVPWM method. Figure 8 C shows the current drawn by the RL load when the PWM module 380 is used. Figure 7 C and Figure 8 It is clear from C that the current drawn by the RL load is smooth and relatively distortion-free when using the PWM module, indicating that there is no significant increase in current harmonics. In other words, Figure 8 B and Figure 8The data in C show that the PWM module 380 maintains good current harmonic performance while reducing CMV.

[0107] These and other implementations are within the scope of the following claims.

Claims

1. A system comprising: Energy storage equipment an inverter electrically coupled to the energy storage device; as well as A pulse width modulation module is configured to: determining a modulation index according to a voltage of the energy storage device and a target output voltage of the inverter; selecting one of a plurality of pulse width modulation (PWM) methods according to the modulation index; and A switching command of the inverter is determined according to the target output voltage and a selected one of a plurality of PWM modulation methods.

2. The system of claim 1, wherein the plurality of PWM methods comprises: Near-end state PWM method, single-mode remote-end state PWM method and dual-mode remote-end state PWM method.

3. The system according to claim 1, wherein: In order to select one of a plurality of PWM methods according to the modulation index, the pulse width modulation module is configured to determine which region of at least two modulation regions the modulation index falls into.

4. The system of claim 1, wherein the at least two modulation regions include a far-end state PWM region and a near-end state PWM region.

5. The system of claim 4, wherein the remote state PWM region comprises: Single mode remote state PWM region and dual mode remote state PWM region.

6. The system of claim 5, wherein each of the near-end state PWM region, the single-mode remote-end state PWM region, and the dual-mode remote-end state PWM region is defined by a corresponding minimum modulation index value and a maximum modulation index value, and the dual-mode remote-end state PWM region is between the single-mode remote-end state PWM region and the near-end state PWM region. 7 . The system of claim 1 , further comprising an energy source electrically connected to the energy storage device, the energy source configured to provide direct current (DC) current to the energy storage device.

8. The system of claim 7, wherein the energy source comprises a rectifier.

9. The system of claim 1, wherein the pulse width modulation module is configured to select one of the plurality of PWM methods according to the modulation index and a setting indicating whether to reduce a common mode voltage.

10. The system of claim 9, wherein if the setting indicates not to reduce the common mode voltage, then the selected one of the plurality of PWM methods is space vector pulse width modulation (SVPWM).

11. The system of claim 9, wherein the setting comprises a value set according to user input.

12. A control system for an inverter, the control system comprising: A pulse width modulation module is configured to: determining a modulation index according to a voltage of an energy storage device in the inverter and a target output voltage of the inverter; selecting one of a plurality of pulse width modulation (PWM) methods based on one or more of the modulation index and common mode voltage settings; Determining a switching instruction of the inverter according to the target output voltage and one of the selected multiple PWM modulation methods; as well as The switching instruction is provided to the inverter, thereby modulating the DC energy in the energy storage device into a driving signal.

13. The control system of claim 12, wherein the pulse width modulation module is configured to select one of the plurality of PWM methods based on the modulation index and the common mode voltage setting.

14. The control system of claim 13, wherein the common mode voltage setting indicates whether to reduce the common mode voltage; as well as If the common mode voltage setting indicates that the common mode voltage is to be reduced, the pulse width modulation module is configured to select one of a plurality of active voltage vector PWM methods according to the modulation index; as well as If the common mode voltage setting indicates not to reduce the common mode voltage, the pulse width modulation module is configured to select space vector pulse width modulation (SVPWM).

15. The control system of claim 14, wherein the plurality of active voltage vector PWM methods include: Near-end state PWM method, single-mode remote-end state PWM method and dual-mode remote-end state PWM method.

16. A method comprising: determining a modulation index according to a voltage of an energy storage device in the inverter and a target output voltage of the inverter; selecting one of a plurality of pulse width modulation (PWM) methods according to the modulation index; Determining a switching instruction of the inverter according to the target output voltage and one of the selected multiple PWM modulation methods; as well as The switching instruction is provided to the inverter, thereby controlling the inverter to modulate the energy in the energy storage device into a driving signal provided to a load. 17 . The method of claim 16 , wherein selecting one of a plurality of PWM methods based on the modulation index comprises selecting one of a near-state PWM method, a single-mode remote-state PWM method, a dual-mode remote-state PWM method, and a space vector pulse width modulation (SVPWM).

18. The method according to claim 17, wherein: For a modulation index less than or equal to 0.906, a common mode voltage generated in the load by providing the drive signal to the load is lower than a common mode voltage generated in the load by controlling the drive signal generated by the inverter based on a switching command determined according to the target output voltage and standard SVPWM.

19. The method according to claim 17, wherein: For a modulation index less than or equal to 0.906, the common mode current generated in the load by providing the drive signal to the load is lower than the common mode current generated in the load by controlling the drive signal generated by the inverter based on the switching command determined according to the target output voltage and the standard SVPWM.

20. The method of claim 16, wherein selecting one of the plurality of PWM methods comprises selecting a PWM method having a linear region including a determined modulation index.

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