Motor Control

Abstract

a conversion unit that calculates a duty cycle corresponding to each of the plurality of pulse-width modulated signals in dependence on the instruction; a gain unit that selects a gain that produces a linear relationship between the required voltage of the pulse-width modulated signal and the voltage achieved by the plurality of pulse-width modulated signals, even when the required voltage of the pulse-width modulated signal is in an overmodulation region, and applies the gain to each of the duty cycles to produce an adjusted duty cycle; and an output unit that outputs the adjusted duty cycle for generating the plurality of pulse-width modulated signals.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to a control device and method. [Background technology]

[0002] A motor control system is shown in Figure 1. The system includes a pulse width modulator (101), an inverter (102), and a motor (103). The voltage demand calculated by a controller (not shown) is converted into pulses by the pulse width modulator. This waveform drives the gate drivers in the inverter.

[0003] Pulse-width modulation (PWM) waveforms are particularly well-suited for driving inertial loads, such as motors. Their inertia causes them to react slowly to changes in the input signal, making them unaffected by the rapidly switching, discrete pulses of a pulse-width modulation signal. Although pulse-width modulation signals are digital, they can function essentially analog when applied to an appropriate load. Two examples of pulse-width modulation (PWM) waveforms are shown in Figure 2 (201 and 202). Both comprise a series of rectangular, on-off pulses. The pulses are generated at a switching frequency. The average voltage of the waveform depends on the percentage of time the pulse is on and the percentage of time it is off. The duty cycle of a PWM waveform is defined as (time the waveform is "high") / (switching period). Waveforms 201 and 202 have the same switching frequency, but because their duty cycles are different, waveform 202 has a higher average voltage than waveform 201.

[0004] One simple way to generate a pulse-width modulated wave is to use a comparator circuit (or other suitable comparator circuit) that accepts a sine wave and a sawtooth wave as inputs and configures it to output either a maximum or minimum circuit voltage, depending on which of the two inputs has the higher value at a particular clock instant. An example is shown in Figure 3. The amplitudes of the carrier triangle wave 301 and the modulating sine wave 302 are compared. If the amplitude of the sine wave is less than that of the triangle wave, the pulse-width modulated signal 303 is set to "low"; if the amplitude of the sine wave is greater than that of the triangle wave, the signal is set to "high." When the sine wave reaches the peak of the triangle wave, the PWM pulse achieves its maximum width. This is shown in Figure 4, where the modulating sine wave 401 exceeds the peak of the carrier triangle wave 402. The modulation is entering saturation.

[0005] A three-phase motor requires three PWM waveforms (one for each coil) that are 120° out of phase with each other. The three waveforms can be generated using the same technique as shown in Figure 2. In this scenario, the maximum line voltage that can be obtained from the PWM waveforms without producing a distorted waveform is (√3) / 2 V. dc , i.e., 86.6% of the DC link voltage. The DC link voltage is underutilized. However, the motor coils see a potential difference, not a point voltage. By appropriately adding / subtracting the three PWM waveforms, we can increase the average voltage of the waveforms without changing the effective voltage between any two waveforms, thereby improving DC link utilization.

[0006] One mechanism for this is Space Vector Pulse Width Modulation (SVPWM). The principle behind this technique is to analyze the state of the motor by considering the voltages per phase as a group. The PWM waveform is a switching waveform directed at six transistors that supply voltage to the motor coils. Each coil is connected to two transistors, and each two-transistor group can be in one of two states: the top transistor is closed and the bottom transistor is open, or vice versa. One state is considered a "1" and the other a "0." Essentially, the switching circuit can be represented by three binary bits, with eight possible output states.

[0007] Rather than viewing it as a problem of generating three independent switching waveforms, a three-phase motor inverter can be viewed as a single unit capable of generating eight different switching states, which are the three-dimensional Cartesian product of two states on phase A, two states on phase B, and two states on phase C. A two-dimensional projection of this configuration is shown in Figure 5. Two states (A,B,C) = (0,0,0) and (1,1,1) represent zero instantaneous line voltages and are often referred to as the "zero" or "null" vector (502). The remaining six states represent non-zero vector voltages applied across the motor terminals (503). These states are called fundamental vectors. The goal of SVPWM is to generate an "average vector" during the PWM period (TPWM) equal to the desired voltage vector 501 (Vout).

[0008] SVPWM can be effectively used in the saturated portion of the modulation domain (also known as the overmodulation domain), which can improve DC-link voltage utilization. However, this is a calculation that is independent of the calculations typically applied in the non-saturated portion of the modulation domain (also known as the linear domain), so the overall PWM technique requires two parts. SVPWM may also require angle calculations to calculate the "mean vector" as a weighted average of the basis vectors. This complicates the duty cycle calculation logic in the motor controller. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, there is a need for an improved mechanism for controlling a motor. [Means for solving the problem]

[0010] According to one aspect of the invention, there is provided a control circuit for generating duty cycles for a plurality of pulse-width modulated signals, the control circuit comprising: an input section for receiving an indication of a desired voltage for the pulse-width modulated signals; a conversion section for calculating a duty cycle for each of the plurality of pulse-width modulated signals in dependence on the indication; a gain section for selecting a gain that results in a linear relationship between the desired voltage for the pulse-width modulated signals and the voltage achieved by the plurality of pulse-width modulated signals, the gain selected such that the linear relationship is maintained even when the desired voltage for the pulse-width modulated signals is in an overmodulation region, and applying the selected gain to each duty cycle to generate an adjusted duty cycle; and an output section for outputting the adjusted duty cycles for generating the plurality of pulse-width modulated signals.

[0011] The gain section may determine whether the voltage required for the pulse width modulated signal is within the linear modulation region, and if so, may apply a gain of one to each duty cycle to generate an adjusted duty cycle.

[0012] The gain unit may be configured to determine whether a voltage required for the pulse width modulated signal falls within an overmodulation region, and if so, may apply a gain other than unity to the respective duty cycle to generate an adjusted duty cycle.

[0013] The control circuit may include an adjustment unit that adds a zero sequence component to the duty cycle calculated by the conversion unit.

[0014] The control circuit may include a flag unit that determines whether the voltage required for the pulse width modulated signal is within the zero sequence injection region.

[0015] The flag unit may be configured to determine that if the voltage required for the pulse width modulated signal is in the linear region, then the voltage required for the pulse width modulated signal is also in the zero sequence injection region.

[0016] The flag unit may determine that when the required voltage is within the overmodulation region, the voltage required for the pulse width modulated signal is within the zero sequence injection region if the voltage is lower than a predetermined threshold, and that the voltage required for the pulse width modulated signal is within the zero sequence injection region if the voltage is higher than the predetermined threshold.

[0017] If the flag unit determines that the voltage required for the pulse width modulated signal is included in the zero sequence injection region, it may add a zero sequence component to the duty cycle calculated by the conversion unit, and if it determines that the voltage required for the pulse width modulated signal is not included in the zero sequence injection region, it may not add a zero sequence component to the duty cycle calculated by the conversion unit.

[0018] The adjustment unit may add the zero sequence component by adding the same amount to each duty cycle calculated by the conversion unit.

[0019] The control circuit may receive an indication of the desired voltage and output an adjusted duty cycle regardless of whether the desired voltage for the pulse width modulated signal is in the overmodulation region or the linear modulation region.

[0020] The number of elements included in the indication of the voltage required for the pulse width modulated signals may be less than the number of the plurality of pulse width modulated signals.

[0021] The indication of the voltage required for the pulse width modulated signal may represent a coordinate in a two-dimensional system.

[0022] An indication of the voltage required for the pulse width modulated signal may be output from the inverse Park transform.

[0023] The converter may use an inverse Clarke transform to convert the indication of the voltage required for the pulse width modulated signal into a respective duty cycle.

[0024] The duty cycle calculated by the transform unit may represent a coordinate in a three-dimensional system.

[0025] The number of the plurality of pulse width modulated signals may be three.

[0026] The gain unit may select the gain by accessing a look-up table.

[0027] The look-up table may be pre-calculated.

[0028] According to one aspect of the invention, there is provided a method for generating duty cycles for a plurality of pulse-width modulated signals, the method comprising: receiving an indication of a desired voltage for the pulse-width modulated signals; calculating, in dependence on the indication, a duty cycle for each of the plurality of pulse-width modulated signals; selecting a gain that results in a linear relationship between the desired voltage for the pulse-width modulated signals and the voltage achieved by the plurality of pulse-width modulated signals, the gain being selected such that the linear relationship is maintained even when the desired voltage for the pulse-width modulated signals is in an overmodulation region; applying the selected gain to each duty cycle to generate an adjusted duty cycle; and an output section for outputting the adjusted duty cycles for generating the plurality of pulse-width modulated signals. [Brief explanation of the drawings]

[0029] The invention will now be described, by way of example only, with reference to the drawings in which:

[0030] [Figure 1] FIG. 1 is a diagram showing an example of a motor control system. [Figure 2] 4A and 4B show examples of low average voltage and high average voltage pulse width modulated signals. [Figure 3] FIG. 10 is a diagram illustrating an example in which a PWM signal is generated. [Figure 4] FIG. 10 is a diagram showing an example of saturation in the generation of a PWM signal. [Figure 5] Diagram showing the eight different switching states in a space vector pulse width modulation representation of a three-phase motor inverter. [Figure 6] FIG. 2 is a diagram showing an example of a control circuit. [Figure 7] FIG. 10 is a diagram showing an example of a control method. [Figure 8] FIG. 1 is a diagram showing an outline of an electric motor arrangement. [Figure 9] FIG. 2 is a diagram showing an example of a motor controller. [Figure 10] FIG. 1 is a diagram showing an example of a three-dimensional coordinate system. [Figure 11] FIG. 1 is a diagram showing an example of a two-dimensional coordinate system. [Figure 12] FIG. 2 is a diagram showing an example of a method for controlling a PWM signal for a three-phase electric motor. [Figure 13] FIG. 10 illustrates the linear relationship between the desired modulation index and the achieved modulation index. DETAILED DESCRIPTION OF THE INVENTION

[0031] An example of a control circuit is shown in Figure 6. The circuit comprises an input section 601, a conversion section 602, a gain section 603, and an output section 604. The circuit is capable of generating duty cycles for multiple PWM signals. The input section is configured to receive an indication of a required voltage for the pulse width modulated signals. The indication may be an average voltage to be met by the combination of the multiple PWM signals.

[0032] The converter 602 may be configured to calculate a duty cycle corresponding to each of the multiple pulse-width modulated signals depending on the instructions. The gain unit 603 is preferably configured to select a gain that results in a linear relationship between the desired voltage and the voltage achieved by the PWM signal. The gain is selected to achieve this linear relationship even when the desired voltage falls within the overmodulation region. The "overmodulation region" may refer to a desired voltage that requires the PWM generation process to enter saturation. For example, the desired voltage may exceed a value that can be achieved by simply increasing the width of the PWM pulse. The gain unit may apply the selected gain to the duty cycles output by the converter to generate adjusted duty cycles. These adjusted duty cycles are then output from the output unit 604 and, if appropriate, supplied to any signal generator capable of generating PWM signals.

[0033] The configuration shown in FIG. 6 (and all block device diagrams contained herein) corresponds to multiple functional blocks within the device. This is for illustrative purposes only. FIG. 6 is not intended to define a strict division between different pieces of hardware on a chip or between different programs, procedures, or functions in software. In some embodiments, some or all of the processes described herein may be performed in whole or in part by hardware. In some implementations, for example, the transform unit 602 and the gain unit 603 may be realized by a processor operating under software control. The software is preferably stored in a non-transitory computer-readable medium, such as memory (RAM, cache, flash, ROM, hard disk, etc.) or other storage means (USB memory, flash, ROM, CD, disk, etc.).

[0034] A suitable method for calculating the duty cycle is outlined in Figure 7. In step S701, an indication of the voltage desired for the pulse width modulated signal is received. This is converted to a respective duty cycle (step S702). To linearize the relationship between the desired voltage and the voltage achieved by the PWM signal, an appropriate gain is selected and applied to the duty cycle to produce an adjusted duty cycle (step S703). The final step is to output the adjusted duty cycle (step S704).

[0035] Each duty cycle can be considered to represent a voltage required for the PWM signal. Therefore, in the following description, these will also be referred to as a "voltage request" to facilitate understanding of the quantity-to-quantity conversion. For example, as a further example, the control circuit may further include an adjustment unit. The conversion unit may be configured to convert the received instruction into a respective duty cycle (or "first voltage request"). The first voltage request may include multiple elements (one element corresponding to each of the multiple pulse-width modulated signals). Each element may be, for example, a scalar or vector quantity. The adjustment unit may be configured to add a zero-sequence component to the first voltage request to generate a second voltage request. The second voltage request is then converted into a third voltage request by a gain unit. This is achieved by multiplying by an appropriate gain to linearize the relationship between the requested voltage and the voltage achieved by the PWM signal. The third voltage request is then output as the duty cycle required for the PWM signal.

[0036] This control circuit can be used in any implementation where a PWM signal is generated. One example is in the field of electric motor control. An overview is shown in Figure 8. In this example, an electric motor 805 is driven by an AC grid 801. The main electrical components are a motor-side converter (motor drive) 804, a DC bus 803, and a grid-side converter 802. The grid-side converter regulates the DC bus voltage, reactive power, and active power, and is required to comply with grid code regulations. The control circuit shown in Figure 6 may be implemented as part of a motor-side control 806 or as part of a grid-side control 807. While the following description focuses on motor-side control, the invention is not limited to this implementation.

[0037] The behavior of an electric motor can be mathematically modeled by considering its voltages and currents. This modeling can be complex because the relative motion of electrical circuits causes continuously changing variables that affect the system's behavior, such as induced voltages, currents, and magnetic flux coupling. For such complex analyses, mathematical transformations are often used to decouple variables and reference time-varying quantities to a common reference frame. Clarke and Park transformations are two commonly used transformations. For example, motor drivers and grid-side converters are often controlled using field-oriented control, in which the three-phase voltages and currents are transformed to dq reference frames using Clarke and Park transformations.

[0038] An example of a motor-side controller is shown in Figure 9. The electric motor is shown at 907. The remaining components 901-906, 908, and 909 are part of a system that controls the motor. The system is configured to independently control the magnetizing and torque-generating components of the stator current using field-oriented control. This requires a series of transforms 904, 905, 908, and 909, which in this example are configured to perform Clarke and Park transforms.

[0039] The motor 907 is a three-phase induction motor and is driven by three PWM signals. The PWM signals are output from a PWM generator 906. The motor phase currents i u , i v and i w is fed back via the transformers 908 and 909. The first feedback transformer 908 uses Clarke transformation to transform the three-phase current i u , i v and i w is expressed as the real / imaginary current component i in a two-dimensional orthogonal system. α , i β The second feedback transformation unit 909 uses Park transformation to transform this two-axis stationary system into a two-axis rotating system i d , i q(i.e., transform from a stationary reference frame to a moving reference frame). The d-axis current can be aligned with the rotor flux, and the q-axis current (torque-producing component) can be orthogonal to the rotor flux.

[0040] The speed controller 901 compares the actual speed of the motor 907 with the desired speed and controls the control current i dref , i qref These may generate feedback current i d , i q The deviation is input to the d-axis controller 902 and the q-axis controller 903. Each of the d-axis and q-axis controllers may be implemented as a proportional-integral (PI) controller. The flux and torque of the stator current are generally controlled independently. Each controller controls the voltage v d , v q These voltages are in a moving reference frame. The inverse Park transform 904 transforms them to a stationary orthogonal reference frame, v α , v β Output.

[0041] The above description refers to an n-dimensional coordinate system. An example of a three-dimensional coordinate system is shown in Figure 10. It includes three mutually orthogonal axes, u, v, and w (1001, 1002, 1003), and defines a cube. If the three-phase voltage of the controller system is normalized, the "coordinates" become three numbers between 0 and 1, and the coordinate system can be represented by a unit cube 1004. In the example of Figure 10, the axes of the cube are stationary, i.e., a three-axis stationary system. Figure 11 shows an example of a two-dimensional coordinate system. It has two mutually orthogonal axes, α and β (1101, 1102), and is a two-dimensional stationary axis system. A hexagon 1103 (the same hexagon shown in Figure 5) is shown superimposed on the axes in Figure 11. This represents the unit cube of Figure 10 as viewed from one of its diagonals. This is an isometric projection, with the vertical axis being the long diagonal of the cube. The Clarke transformation essentially reproduces the transformation between the unit cube of Figure 10 and the hexagon of Figure 11. The Clarke transformation maps the phase-separate components u, v, and w (a three-dimensional system) onto a two-dimensional plane consisting of two components, α and β.

[0042] Returning to the control system of FIG. 9, v generated by the conversion unit 904 α , v β can be considered to represent coordinates in a two-dimensional system with orthogonal axes α and β. In the SVPWM system, the time-invariant coordinates v α , v β can be used directly to generate three-phase voltages. The number of elements here is one less than the number of required duty cycles. A third element can be introduced by also considering the angle. For example, as shown in Figure 5, the "mean vector" can be calculated as a composition of multiple basis vectors. In the control system of Figure 9, the transformation unit 905 instead calculates v α , v β The phase-specific voltage component v u , v v and v wThese phase-specific voltage components can be considered to represent coordinates in a three-dimensional system as shown in Figure 10. Since there are three elements, one element can be assigned to each phase of the motor. Voltage v u , v v and v w is output to a PWM generator 906 and the resulting PWM signal is supplied to an electric motor 907.

[0043] A detailed breakdown of the processing that may be performed by the converter 905 is shown in Figure 12. This diagram relates to a particular implementation and is provided for illustrative purposes only, and includes steps that are not essential for successful operation and may be omitted or substituted in other implementations.

[0044] The transform unit 905 converts the value V β_dem and V α_dem These values ​​are indicators of the voltages ultimately required for the PWM signals. In this example, the motor is three-phase, so the number of PWM signals is also three. The indicators received are: V β_dem and V α_dem V β_dem and V α_dem can also be thought of as representing coordinates in a two-dimensional system (e.g., as shown in Figure 11).

[0045] Voltage requirement V β_dem and V α_dem First, the DC link voltage V dc This divides the value into two values ​​V between 0 and 1 and scales it to a value per unit (step S1201). β_dem_pu and V α_dem_pu These values ​​are converted to voltages with a three-dimensional representation using the inverse Clarke transform (step S1203). This calculation can be expressed as follows:

number

number

number

[0046] The control circuit is configured to add a zero-sequence component to the inverse Clarke transform output voltage (step S1206). Figure 11 is a plan view of the cube of Figure 10, a two-dimensional projection of a three-dimensional system. A planar projection of a three-dimensional system surrenders one degree of freedom perpendicular to the viewing plane. In this case, adding a zero-sequence component to any point within the cube does not affect the position of that point in the projection of Figure 11. The viewing plane of Figure 11 represents the voltage "seen" by the motor. The zero-sequence component does not affect the phase-to-phase voltages, but it does increase the combined three-phase voltage, thereby increasing the utilization of the DC link. In step S1206, the same voltage is applied equally to each phase. The resulting value can be considered to constitute the second voltage demand.

[0047] The zero sequence component is used in both the linear transformation domain and the overmodulation domain. In the linear transformation domain, the zero sequence component is used to achieve a voltage equivalent to the maximum (linear) voltage achieved using SVPWM modulation. In the overmodulation domain, the zero sequence component is injected depending on the required modulation index.

[0048] From Figure 12, V amp_dem_pu_sqr = 0.333 is M dem = 1, which corresponds to V amp_dem_pu_sqr = M dem 2 This is because V amp_dem_pu_sqr<= 0.333, the technique of Figure 12 operates in the linear transform domain. gain = 1 and the zero sequence is included in the duty cycle calculation. amp_dem_pu_sqr > 0.333, the technique operates in the overmodulation region, but below the threshold where zero sequence injection becomes ineffective. gain is V amp_dem_pu_sqr The zero sequence is injected depending on V amp_dem_pu_sqr > 0.371, zero sequence may not be used. When M = 1.055, the duty cycle waveform may become "trapezoidal". M = 1.055 may be the boundary between two sections of the overmodulation region. Above M = 1.055, zero sequence injection will not be beneficial for trapezoidal waveforms. This causes P gain is selected from a lookup table, resulting in an overmodulation region where no zero sequence is injected. Above M = 1.1, this is typically the 6-step operating region.

[0049] For example, the zero sequence component may be injected as follows:

number

number

number

[0050] One suitable technique for introducing zero sequence components is to inject harmonics of the operating frequency to increase the line voltage. For example, a triangular wave with a frequency three times the fundamental frequency may be injected as zero sequence. This injection affects the voltage to ground but not the line voltage because the third harmonic of each phase is the same. Zero sequence injection can be expressed as:

[0051]

number

[0052] The control circuit includes a flag unit that determines whether the required voltage is within the zero sequence injection region (step S1206). zero Setting t to 0 or 1 controls whether a zero sequence is added to the output of the inverse Clarke transform.

[0053] When the three-phase composite voltage demanded by the controller exceeds the range that can be achieved by simply increasing the width of the PWM pulses (see, for example, FIG. 4 and related discussion), the control circuit can be considered to be operating in the overmodulation region. dem is the desired modulation index, M achieved represents the achieved modulation index. The modulation index is defined as follows:

number

[0054] When 0 < M < 1, there is a linear relationship between the voltage required by the controller and the modulated voltage of the PWM signal. Outside this range is the overmodulation region, where the linear relationship breaks down due to saturation. This results in a control mismatch. To address this, the control circuit applies a gain to the output voltage of the inverse Clarke transform. The gain may be selected from a lookup table (step S1104). In one implementation, the gain is selected from a one-dimensional lookup table based on the square-scaled voltage amplitude. The gain lookup table is preferably calculated appropriately in advance. Each gain is determined by M dem and M achieved It is preferable to set the relationship between M to be linear. dem If V is in the linear transformation domain, the lookup table may simply output a gain of "1". U_dem_pu, V V_dem_pu , V W_dem_pu This applies to all three components.

[0055] Finally, the control circuit checks the obtained voltages for saturation issues and corrects them if necessary (step S1207). In this example, the obtained values ​​are normalized by the DC link voltage (see step S1201). Therefore, they are used to calculate the required duty cycles r of the three PWM signals. u_duty , r v_duty and r w_duty In other implementations, various "voltage requirements" may indirectly represent duty cycles. These can be used to generate pulses that drive the gate drivers of the motor controller. These can be considered a third voltage requirement in this implementation.

[0056] The terms "first," "second," and "third" voltage requirements may apply to different values ​​depending on the implementation. The usage in the above implementations is for illustrative purposes only and should not be limited to specific values ​​or steps.

[0057] The appropriate gains will typically not change for different motors and / or vehicles, and therefore can be calculated in advance rather than having to be tuned for different motors or vehicles.

[0058] An example of a method for calculating the lookup table is shown below. It should be understood that various approaches are possible for calculating the lookup table, and this description is a description of a specific implementation example. Even with other methods, it is possible to calculate the M dem and M achieved A table can be generated that linearizes the relationship within an acceptable range.

[0059] The lookup table may be divided into two segments. The first segment of the lookup table is amp_dem_pu_sqr P for <= 0.371 gain Gives (V amp_dem_pu_sqr<= 0.333, the modulation is in the linear transform domain as described above. gain The value of may be calculated by the following procedure. 1) In the method shown in Figure 12, P gain = 1. 2) Given V dc For v as follows: α_dem and v β_dem Give.

number

[0060] Then, for each M dem For a given process, the duty cycle r u_duty , r v_duty and r w_duty The modulation index M achieved from achieved This calculates M dem and M achieved You can create a table to compare the following. The table below is an example. step = 0.001. [Table 1]

[0061] Based on the values ​​in Table 1, an acceptable R value reflecting the fitting accuracy is 2 Fitting equation with value P gain = f(M achieved ) can be obtained.

[0062] 3) To linearize the overmodulation region, P gain Correct the duty cycle calculation using M dem = M achieved So that it becomes. M dem = M achieved Assuming that, V amp_dem_pu_sqris M dem 2 / 3. Therefore, based on this fitting equation, P gain and V amp_dem_pu_sqr We can establish the relationship between V in the interval (0.333, 0.371] amp_dem_pu_sqr One-dimensional P for gain The lookup table can be generated to have any number of breakpoints.

[0063] To calculate the second segment of the 1D lookup table, 0.371 < Vamp_dem_pu_sqr <= 0.405, we apply the same method but change the sweep range of Mdem from (1, 1.154] to (1.154, 1.256].

[0064] One aspect of the motor control circuit's performance is shown in Figure 13. The graph plots Mdem versus Machieved. The two are linearly related, even in the overmodulation region 1301. This linearization reduces the discrepancy between the desired and achieved voltages, improving motor control accuracy. Extending linearization into the overmodulation region preserves these control benefits while increasing DC link utilization. This allows for larger three-phase voltage outputs, potentially resulting in greater torque / power output for the same DC link voltage. Approximately 10% higher voltage outputs can be achieved compared to existing linearized methods. This is particularly useful for motor control in the automotive and motorsport industries. It extends the motor's operating range while reducing dynamic response time. Additionally, it reduces the field-weakening current required at high speeds. Overmodulation provides additional voltage output capability. At high speeds, the motor requires slower field-weakening current than linear modulation to maintain voltage within its voltage output capability.

[0065] Therefore, the control circuit can calculate the three-phase duty cycles ru_duty, rv_duty, and rw_duty from the voltage demands Vβ_dem and Vα_dem by implementing the process shown in Figure 12. The control circuit performs this calculation regardless of whether the voltage demands are in the linear transformation domain or the overmodulation domain. In fact, the main processing in both modulation domains is identical. The differences between the domains are handled by gain selection (e.g., a gain of "1" in the linear transformation domain) and the setting of the zero sequence flag. This results in very good integration between linear modulation and overmodulation. This results in reduced complexity compared to solutions that require separate processing for the two domains.

[0066] A control circuit that calculates the required duty cycle of a three-phase signal to drive an electric motor may be configured to apply a gain to linearize the relationship between the required voltage and the voltage achievable by the signal. This circuit is simpler and easier to implement than existing designs. Because all calculations are arithmetic, it is compatible with a variety of processors and can operate at high frequencies.

[0067] The applicant discloses each feature described in this specification, either alone or in any combination of two or more features, to the extent that such feature or combination can be implemented based on the entire specification in light of the techniques known to those skilled in the art, regardless of whether such feature or combination solves the problems disclosed in this specification or limits the scope of the claims. The applicant suggests that aspects of the present invention may consist of each such individual feature or any combination thereof. From the above description, it will be apparent to those skilled in the art that various modifications within the scope of the present invention are possible.

Claims

1. 1. A control circuit for generating duty cycles of a plurality of pulse width modulated signals, comprising: an input for receiving an indication of a desired voltage for said pulse width modulated signal; a conversion unit that calculates a duty cycle corresponding to each of the plurality of pulse width modulated signals in dependence on the instructions; a gain section that selects a gain that produces a linear relationship between the voltage required for the pulse width modulated signal and the voltage achieved by the plurality of pulse width modulated signals, even when the voltage required for the pulse width modulated signal is in an overmodulation region, and applies the gain to each of the duty cycles to produce an adjusted duty cycle; an output for outputting the adjusted duty cycle for generating the plurality of pulse width modulated signals; A control circuit comprising:

2. The gain section determining whether the voltage required for the pulse width modulated signal is within a linear modulation region; if it is determined that the voltage required for the pulse width modulated signal is within a linear modulation region, applying a gain of one to each of the duty cycles to generate the adjusted duty cycles.

2. The control circuit of claim 1.

3. The gain section determining whether a voltage required for the pulse width modulation signal is within the overmodulation region; applying a gain other than unity to each of the duty cycles to generate the adjusted duty cycles when it is determined that the voltage required for the pulse width modulated signal is within the overmodulation region.

3. The control circuit according to claim 1 or 2.

4. an adjustment unit that adds a zero sequence component to the duty cycle calculated by the conversion unit; 4. The control circuit according to claim 1, comprising:

5. a flag unit that determines whether a voltage required for the pulse width modulation signal is within a zero sequence injection region; 5. The control circuit according to claim 1, comprising:

6. the flag unit determines that the voltage required for the pulse width modulation signal is also included in the zero sequence injection region when the voltage required for the pulse width modulation signal is included in a linear region; 6. The control circuit of claim 5.

7. When a voltage required for the pulse width modulation signal is included in the overmodulation region, the flag section determining that the required voltage of the pulse width modulated signal is within the zero sequence injection region if the required voltage of the pulse width modulated signal is less than a predetermined threshold; determining that the voltage required for the pulse width modulated signal is within the zero sequence injection region if the voltage required for the pulse width modulated signal exceeds the predetermined threshold; 7. The control circuit according to claim 5 or claim 6.

8. The flag section if it is determined that the voltage required for the pulse width modulated signal is included in the zero sequence injection region, adding the zero sequence component to the duty cycle calculated by the conversion unit; If it is determined that the voltage required for the pulse width modulation signal is not included in the zero sequence injection region, the zero sequence component is not added to the duty cycle calculated by the conversion unit. A control circuit according to any one of claims 5 to 7.

9. the adjustment unit adds the zero sequence component by adding the same amount to each duty cycle calculated by the conversion unit; A control circuit according to any one of claims 1 to 8.

10. receiving an indication of a desired voltage for the pulse width modulated signal, and outputting the adjusted duty cycle regardless of whether the desired voltage for the pulse width modulated signal is in an overmodulation region or a linear modulation region; A control circuit according to any one of claims 1 to 9.

11. the number of elements included in the indication of the voltage required for the pulse width modulated signal is less than the number of the plurality of pulse width modulated signals; A control circuit according to any one of claims 1 to 10.

12. an indication of the voltage required for said pulse width modulated signal represents a coordinate in a two-dimensional system; A control circuit according to any one of claims 1 to 11.

13. an indication of the voltage required for said pulse width modulated signal being the output from an inverse Park transform; A control circuit according to any one of claims 1 to 12.

14. the converter converts the indication of the voltage required for the pulse width modulated signal into the respective duty cycle using an inverse Clarke transform; A control circuit according to any one of claims 1 to 13.

15. The duty cycle calculated by the conversion unit represents a coordinate in a three-dimensional system. A control circuit according to any one of claims 1 to 14.

16. the number of the plurality of pulse width modulated signals is three; 16. A control circuit according to any one of claims 1 to 15.

17. the gain unit selects the gain by accessing a lookup table.

17. A control circuit according to any one of claims 1 to 16.

18. the lookup table is pre-calculated; 18. A control circuit according to any one of claims 1 to 17.

19. 1. A method for generating duty cycles of a plurality of pulse width modulated signals, comprising: receiving an indication of a desired voltage for said pulse width modulated signal; calculating a duty cycle for each of the plurality of pulse width modulated signals in dependence on the instructions; selecting a gain that produces a linear relationship between the voltage required for the pulse width modulated signal and the voltage achieved by the plurality of pulse width modulated signals, even when the voltage required for the pulse width modulated signal is in an overmodulation region, and applying the gain to each of the duty cycles to produce an adjusted duty cycle; outputting the adjusted duty cycle for generating the plurality of pulse width modulated signals. method.

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