PWM signal generator and motor vehicle with an electric motor that can be controlled with such a PWM signal generator

Abstract

The invention relates to a PWM signal generator for generating PWM control signals for controlling an inverter for a three-phase or multi-phase motor, comprising a microcontroller for generating control signals at microcontroller signal outputs and multiple PWM signal outputs. According to the invention, several microcontroller signal outputs are combined into a common PWM signal output at each of the PWM signal outputs.

Description

[0001] The invention relates to a PWM signal generator for generating PWM control signals for controlling an inverter for a three-phase or multi-phase motor.

[0002] Modern microcontrollers used for motor control typically employ pulse width modulation modules (PWM modules).

[0003] In pulse-width modulation, also called pulse duration modulation, the control signal, for example the control voltage, is switched back and forth between two values ​​with a constant period. There is therefore a high value and a low value between which the control signal alternates. The square wave signal has a constant frequency, and the duty cycle, i.e., the duration of the square wave pulse, is modulated.

[0004] To set the period and duty cycle of the control signal in the aforementioned modules, counters with associated registers are usually provided, in which the times for switching on and off the control voltage are stored.

[0005] The automotive industry frequently uses electric motors with three or more phases. These are typically controlled by an inverter circuit with two switching elements for each phase. This allows each phase to be connected to either the high or low signal. The switching elements—for example, IGBT or MOSFET components—are controlled by PWM signal generators. These usually include microcontrollers designed to switch the corresponding microcontroller signal output twice within the PWM cycle—once on and once off. This switching frequency is sufficient for most applications, such as space vector modulation or, alternatively, for discontinuous PWM methods. Other modulation methods, however, such as OPP (Optimized Pulse Patterns), require multiple switching operations within a single PWM cycle.This could be achieved by the microcontroller providing a higher switching frequency, but this is generally not possible with microcontrollers currently on the market. Alternatively, faster switching controllers such as FPGAs or CPLDs can be used, but this significantly increases the cost of the PWM signal generator.

[0006] It is an object of the invention to provide a PWM signal generator that provides more switching operations per PWM period without incurring higher costs for faster switching controllers.

[0007] This problem is solved by the subject matter of independent claim 1.

[0008] The PWM signal generator according to the invention for generating PWM control signals for controlling an inverter for a three-phase motor comprises a microcontroller for generating control signals at microcontroller signal outputs and three PWM signal outputs. According to the invention, several microcontroller signal outputs are combined into a common PWM signal output at each of the PWM signal outputs. In this way, several switching operations can be triggered at the combined PWM signal output during one PWM period without having to increase the clock frequency of the microcontroller.

[0009] In a preferred embodiment, the microcontroller is designed to combine at least three microcontroller signal outputs into one PWM signal output. In this way, six switching operations can be performed during one PWM period instead of two.

[0010] In one specific embodiment, the PWM signal generator comprises multiple multiplexers, each with multiple multiplexer inputs and one multiplexer output. A multiplexer allows the multiple microcontroller signal outputs to be easily combined into a common PWM signal output. In one embodiment, a multiplexer can be implemented with discrete OR logic gates, optionally cascaded according to the number of multiplexer inputs.

[0011] Specifically, it can be provided that several microcontroller signal outputs are connected to the corresponding multiplexer input and / or that the respective multiplexer output is connected to the PWM signal output of the PWM signal generator.

[0012] The task is also solved by a motor vehicle in accordance with the independent subsidiary claim.

[0013] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. These show: Fig. 1 an inverter circuit; Fig. 2 an embodiment of a PWM signal generator; Fig. 3 a diagram for generating a PWM signal; and Fig. 4. A diagram illustrating the generation of a complex PWM signal.

[0014] Fig. Figure 1 illustrates a known three-phase inverter circuit 10 in a circuit diagram. This is merely an example – inverter circuits for more than three phases can also be implemented. The inverter circuit 10 includes a DC power source U. BAT, whose circuit can be closed or opened with a switch S. For controlling a motor, the inverter circuit 10 comprises three half-bridges, namely a first half-bridge 12 with two power semiconductor switches 14, 16, each connected in parallel with a freewheeling diode 18, 20, a second half-bridge 22 with two power semiconductor switches 24, 26, each connected in parallel with a freewheeling diode 28, 30, and a third half-bridge 32 with two power semiconductor switches 34, 36, each connected in parallel with a freewheeling diode 38, 40.

[0015] The voltages U, V, W are applied in the middle of the half-bridges 12, 22, 32, which are U relative to N. BAT / 2 or - U BAT / 2. It would also be possible to refer the voltages to a ground, then either U would be BAT or mass is present.

[0016] These voltages U, V, W are transmitted to a three-phase motor 50, represented here by a three-phase load with three resistive loads 42, 44, 46. To drive this motor 50, the switches 14, 16, 24, 26, 34, 36 must be controlled accordingly. This is done by means of a PWM signal generator, as shown in Fig. 2 is shown.

[0017] Fig. Figure 2 illustrates a PWM signal generator 100 in a schematic diagram. The PWM signal generator 100 has PCB signal outputs 102, 104, 106 and a microcontroller 110. In this context, a microcontroller 110 is understood to be a component that includes a processor and peripheral functions. For example, a microcontroller can have one or more CPUs, memory, and programmable output pins. These functions are typically implemented on a single chip in microcontrollers.

[0018] The in Fig. The illustrated microcontroller 110 is optimized for outputting PWM signals and includes the necessary components. In the illustrated embodiment, the microcontroller 110 has nine output pins 112-128. At each of these pins, the microcontroller 110 is capable of switching the applied signal twice during one PWM cycle.

[0019] Fig. Figure 3 illustrates the generation of a PWM signal within the microcontroller 110. The diagram shows time on abscissas 130 and 131, while the ordinate 132 is divided into two parts. The upper part of the ordinate 132, corresponding to abscissa 130, displays a counter value. The part of the ordinate 132, corresponding to abscissa 131, displays a control voltage value HS. The counter values ​​c plotted on the ordinate 132 ON , c OFF and c MAXThe following meaning applies: When the corresponding subroutine starts with the ISR interrupt (time 134), the associated counter register (not shown) is incremented. If this register reaches the value c at time 136... ON , a corresponding control signal is output by applying the high value of the control voltage HS, see reference numeral 138. When the counter register reaches the value c OFF At time 140, the control voltage is set back to zero or the corresponding low value, see reference numeral 142. Upon reaching the count value c MAX At time 144, the PWM period Ts is reached and the counter register is reset. This process repeats with the immediately triggered ISR for each PWM period.

[0020] In Fig. 2. These control signals / voltages for each output 112-128 are designated accordingly with "PWM_U1 ... PWM_U3" as the PWM control signal for the motor voltage U, with "PWM_V1 ... PWM_V3" for the motor voltage V, and with "PWM_W1 ... PWM_W3". The microcontroller outputs 112-128, to which these control signals are applied, are connected to multiplexer components 150, 152, and 154. Three microcontroller outputs (112 / 114 / 116, 118 / 120 / 122, 124 / 126 / 128) are connected to multiplexer components (150, 152, 154) and their corresponding inputs (160 / 162 / 164, 166 / 168 / 170, 172 / 174 / 176). The input signals, in the form of PWM control signals, are combined by multiplexer 150, 152, 154 into output signals PWM_U, PWM_V, and PWM_W. These output signals are then present at outputs 156, 157, and 158 of multiplexer 150, 152, and 154, respectively, and also at the corresponding PWM signal outputs 102, 104, and 106. This process is in Fig. 4 illustrates.

[0021] Fig. Figure 4 shows a schematic diagram of the conversion of the three input control signals PWM_U1, PWM_U2, and PWM_U3 into a single output control signal PWM_U. The left side of the diagram shows the signals PWM_U1 ... PWM_U3 over time during one PWM period Ts. These signals are combined into a single control signal PWM_U by the multiplexer component, as shown on the right side of the diagram. The individual signals PWM_U1 ... PWM_U3 are summed to form a single signal PWM_U. In this way, by extending the microcontroller 110 with the multiplexer components 150-154, multiple switching operations can be performed during one PWM period Ts without having to increase the clock frequency of the microcontroller 110. The number of three inputs for the multiplexers 150-154 for combining the PWM signals PWM_U1 ... PWM_U3 to PWM_U is chosen here as an example.In another embodiment, more or fewer microcontroller output signals can be combined to form a PWM control signal.

[0022] Furthermore, the Fig. Figure 4 shows an exemplary embodiment 200 of a multiplexer component 150, discretely constructed from OR gates 202 and 204. The OR gates 202 and 204 illustrate an exemplary embodiment in which three inputs 206-208, which receive the signals PWM_U1-PWM_U3, are mapped to an output 212 with the signal PWM_U. This construction is merely exemplary; a multiplexer component 150 can also be constructed from other discrete components.

Claims

[1] PWM signal generator (100) for generating PWM control signals for controlling an inverter (10) for a three-phase or multi-phase motor (50), with a microcontroller (110) for generating control signals at microcontroller signal outputs of the microcontroller (110) as well as multiple PWM signal outputs, characterized by , that at the PWM signal outputs (102) several microcontroller signal outputs (112, 114, 116) are combined to form a common PWM signal output (102). [2] PWM signal generator according to claim 1, wherein the microcontroller (110) is designed to combine at least three microcontroller signal outputs (112, 114, 116) to form a PWM signal output (102). [3] PWM signal generator according to one of the preceding claims with multiple multiplexers (150, 152, 154), wherein each multiplexer (150) has multiple multiplexer inputs (160, 162, 164) and one multiplexer output (102). [4] PWM signal generator according to claim 3, wherein several microcontroller signal outputs (112, 114, 116) are connected to the corresponding multiplexer input (160, 162, 164). [5] PWM signal generator according to one of claims 3 or 4, wherein the respective multiplexer output (156, 157, 158) is connected to the PWM signal output (102, 104, 106) of the PWM signal generator (100). [6] PWM signal generator according to one of the preceding claims, wherein the PWM signal generator (100) has three PWM signal outputs (102, 104, 106).

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