I am part of a team designing an electric car and we decided to use a bldc and I need to decide to use square wave or a sine wave controller. Since we have a cooling issue I must know which type of inverters generally dissipates more heat square wave or pure sine wave (same power rating)? I think it's the pure sine wave because of higher mosfet switching frequency and passive filters used, but I am not sure if I am right.
In an inverter, each switching event loses some energy in the inverter. You therefore need to minimise the switching frequency in order to maximise inverter efficiency. This means (a) square wave output rather than sine and (b) lowest frequency waveform.
You probably don't want to maximise inverter efficiency. You probably want to maximise system efficiency, which includes the motors.
The output torque of the motors is proportional to current. The motor winding \$I^2R\$ loss is proportional to current squared. This means that the motors will run more efficiently with a low ripple current (like you get from a sine output converter) than with a high ripple current.
A low ripple current requires either a faster PWM'ing inverter, or a filter between inverter and motor, or both.
Square wave -> efficient inverter, inefficient motors
Sine wave -> inefficient inverter, efficient motors
To get best overall system efficiency you probably need to use a custom inverter, and adjust it to your motor parameters, while measuring the performance of the system as a whole.
Square wave inverter will be somewhat more efficient than a sine wave inverted.
The square wave inverter switches at the same frequency as the AC which it generates. The pure sine wave inverter switches at a much higher frequency and modulates (PWM) the duty cycle such that the duty cycle in a sine function. Additional power is dissipated during each switching event.
The inverters which are intended for driving AC motors usually go under the name Variable Frequency Drive (VFD).
Don't know about square wave inverter output. Did you mean, six step pulse control for BLDC? If so, and this is the only control method for BLDC that outputs square wave, then it might be useless, since your car will be always accelerating with maximum acceleration until reaching the final speed. Therefore no speed control, which indeed has to be implemented in a car/bike drive.
If you want to add the speed control, then here it comes the PWM output. Still you might have six step pulse or three phase sine wave output. So you might exclude the square output from further calculations.